You'll need a few minimum basic fabrication tools;
- small angle grinder with cutting and grinding discs
- drill with a few bits; 6, 8, 12mm (the 6mm is for piloting holes)
- jigsaw
- welder (either mig or stick) capable of welding up to 4mm
- a hammer and a couple of small pin punches and a dot punch
- a couple of files; a half round and round will do
- a big hammer
- a rule, marking tools and a tape measure
A few other tools that are pretty useful (but not essential);
Slitting blades for a small (4.5 inch) grinder, they're thinner than a normal cutting blade and so quicker. You'll probably have to go to a proper industrial supplier, the local DIY superstore more n likely won't stock em.
A 9inch grinder is well useful, saves so much time and effort (sorry for the upside down photo, the uploader seems to hate this particular photo and won't show it any other way no matter the orientation of the original - sodding technology huh?)
And slitting blades to match, BE CAREFUL, these puppies chew through steel like a hot knife thru butter. They will not hesitate to take fingers off. You have been warned.
And a flap wheel for the small grinder is nice to have, just makes cleaning off paint and smoothing edges a hell of alot easier n quicker.
Oh yeah, plenty of sweat and swearing are useful, as are plasters.
First you'll have to decommission (de-gas) your gas bottle, if you need me to tell you how to do it then you probably shouldn't be doing it. l'm not gonna go all 'elf n safety' on you but it can be dangerous, you're messing about with explosive gas in a sealed container (a.k.a. bomb). Random fact for you; at -5degrees propane/butane becomes a heavy oily gas that doesn't dissipate easily and just sits around on your patio waiting for a smoker to walk around the corner, that was (personally) an interesting (read nerve wracking) day :P
I usually use a 15kg bottle, it kicks out enough heat for a decent size room. I will do an instructional on a bigger one later but "he's" a bit special and not for now. The door sizes are a balance between useability and access. You need a decent size door for filling, too small a door and you can only fit twigs in and you have to fill it every 20min. Too big a door and your ashpan door is too small as is the grate, and the fire blows out all the smoke as soon as you open the door.Once you've chopped out the carcass clean off all new edges, l know it sounds a little anally-retentive but you're gonna be throwing this thing around on the workbench for the next few days and you'll slice yourself up pretty good. l know, trust me.
Okay, now you need to chop out a fake floor for the beast, anything above 2mm will do, as it doesn't really take any direct heat. It's just to support the ashpan and fire grate. The diameter needs to be slightly (and only slightly) smaller than the internal diameter of the carcass. When you drop it in it should just sit slightly into the bottom curve on the bottle. When your happy with it then stitch weld it in. You should just about be able to see from the photo that the base plate/ fake floor sits about 10mm below the bottom edge of the bottom doorway, this small ledge minimises the amount of ash that is dragged out when you pull out the ashpan.Now for the construction of the grate, l used to use old cast iron fire grates from the local reclamation yard but they are getting harder to find and also more expensive so now l just make em from 10mm square bar. lt's easy enough if a little time consuming.
l favour the lazy mans method of bending bar, l really can't be a&*)d to fire up the forge to bend a few bits.
The method is simple really; cut through the bar till it's almost all the way, leave about a mil, smack it with a hammer, weld up the new gap. Simples. l swear l just heard a meerkat squeak! That damn advert is like a mind worm, meh.
Now to start making up the grate, make 2 base supports. Try to get em level and straight and weld the ends to the base plate.
If you thought that was a little entertaining your gonna love this next bit (not).You'll need to make up your first grate bar, bend either end (lazy man style) to about 45 degrees with about 30mm turn-up on either end. The turn-up on the back stops the fire resting against the sidewall of the bottle so stopping/slowing burn-out. Also the rear turn-up is a few mil away from the sidewall. The front turn-up holds the fire on the grate, you can probably see from the photo that the bar is short of the door. l've found with the fire set back a little from the door you get less smoke with the door open. Well that's my reasoning and l'm sticking to it, hehe. 
Here l've made a small T-bar for spacing the grate bars (ignore the turn-up on the end, it's a piece of scrap l had lying on the bench). It just makes life easier and gives a nice effect.
You can see how the T-bar is used here, The spacing is far from critical but it looks better when it's even.
And repeat, keeping the rear turn-up just slightly shy of the rear wall. Shortening each bar a tad.
It's easier to just tack weld the top plate in position at this point, it saves it floating about when your trying to get other pieces to fit. Mark, chop, fit the upright plate as well but don't tack it yet, you haven't finished with the top yet.
A side view, duh.
Now for some fun, now you've got your top plate it's now time to sort out the porting. It's not entirely necessary to port the stove, or some people seem to think so, but you lose alot of heat and end up with a greedy and crap stove which barely melts chocolate if you don't.
Here you'll need some 4 or 5inch steel pipe with a minimum 4mm wall thickness. It MUST be steel - cast won't put up with what you're gonna do to it next, if you don't know if it's cast or not then there's a simple test (did you just hear a meerkat squeak?) Wearing glasses and gloves ("it's elf n safety gov'nr") with a big hammer belt the edge of your pipe, are you know picking shards out of your legs? Did the pipe practically shatter? If you answer yes to either then it was cast, it's brittle. Did it just give a nice high pitch ring and bend slightly? If you now answer yes then it's more n likely steel and you now want a 9inch piece of it (sorry about switching between metric and imperial measurements, when l was a college n uni' we where in the changeover so needed to know both). Simple trick here, use abit of electrical tape to mark out your cutting line, it's easy (with a little practice) to get a nice straight mark around a pipe.
Before you cut all the way round, slit the piece from end to end, it's easier doing it now than trying to hold a small workpiece in the bench and stop it from twisting. If you're using slitting blades BE CAREFUL, if the workpiece twists or you twist the grinder the blade will snatch and possibly explode. l've ended up picking bits of disc out of my face, these bad boys don't mess about.
Now it's big hammer time (wasn't that a really cool eighties song? And why can l hear Tweek from Southpark singing it?). If you haven't got an anvil (yeah yeah, l've heard some people don't, unbelievable huh?), then a decent paving slab will do or a breeze block. At this point your nieghbours are really gonna love you, mine love me - honest .. ... Oh, word to the wise, don't do it on your nice new patio, it'll look like it's been chewed on by a large troll when your finished. The soon to be Ex-wife won't like it, oops.
You'll need to flatten out the pipe, that's what the hammer n anvil are for. It would be easier n smarter to use a blow torch or forge, but if you don't have either, or like making lots of noise then this method works. What you're after is a gently curved section of the pipe, wide n shallow is best. [Actually this worked out to be a little too shallow, still works but inhibits the draw slightly, so make it deeper by a tad.] And then ... ...
You need to shape the back edge of the curved vent so it sits snugly against the back wall of the cylinder.
Hmmm, not the best photo, but trust me, it fits.
And tack it into place.
At this point l find it easier to make cardboard patterns for the semi-circular infill plates. Again use 4mm, they take alot of heat. Chop n tack em to the top plate and port only - NOT the bottle. Grind off the tack welds holding the top plate to the bottle and you should end up with something like ... ... ...
From above,
and underneath.
Now fully seam weld the piece together, really burn the welds in, they take alot of stress.
And then fully seam weld the whole porting plate into position.
Both from above AND below. Now you can see how well the porting tube fits against the backwall of the bottle - told ya.
You'll know if you've really got the welds to burn in, the paint will burn off from the other side.
Now grind the exposed welds back till they look pretty, it's one reason why l seam from above and below.
Now the carcass is starting to look like a stove, so on to the doors.
l chop these from another bottle, making sure they overlap the hole by at least 15mm on all sides. My donor bottle in this case was one of the large ones and the curvature is slightly different, as can be seen below.
A little gentle (snigger) attention with a large hammer and it will soon fit.
For the hinges l use old motorcycle chain, l get mine from a local friendly bike shop (cheers Sharky). Get a decent beefy one, make sure it comes off a big bike. Grind off the swaged end of the pin and then punch it out with a pin punch.
l use four links, it's probably overkill but l want the hinges to last. Tack weld em in position first and try to get them as parallel and level as possible. Open n shut the door a few times to check on the movement, a little stiffness is ok - they'll bed in after a few heats. If your happy enough (you'll never be completely happy with em, but you can spend days hung on this stage if you 'faff' too much), then burn em in good n proper. If all fails, then a good 'talking to' with a large hammer usually works :)
Now for the ashpan door/ vent. l find it easier to use abit of basic math (did l just hear someone scream in pain??). Just try and wade through it, l find it fun but then l enjoy quadratics and differentiation. Yeah yeah, l know l need to get out more, but it takes so long to chew thru the straps :P
Pilot drill and then jigsaw out the holes to whatever the formula gave you.
So you end up with.
The idea is ... ...
So now you need to mark and chop out the sliding vent plate.
Here you can use the piece you chopped out to make the actual slider plate. The width of the vent 'triangles' is the same as whatever the formula gave out. So you should end up with .. ..
Mark out the vent holes, pilot drill with a big enough drill to provide clearance for your jigsaw blade and then cut them out (or use a plasma cutter if your lucky enough to have one). And repeat ... ... ...
Once you grind the paint off it should look something like ... ... ...
Now you'll need four strips around 10mm wide by the length of the door of bottle thickness steel, l usually chop em out of the piece you cut out to make the upper feed door, you'll also need two strips of 10mm wide by door length by 1mm thick. I know it's as clear as mud but the diagram might help, l forgot to take a photo (oops).
I know it's not massively clear but if you think it through it does make sense and you should end up with this ..
Okay the next bit is pure detail (eg. not essential ) however, the devil is in the details as my gran always said.
Here I use a small offcut of something, you'll usually find something on the bench somewhere, weld it (on 3 sides only - the unwelded edge is what the door butts up against) in order to stop the sliding door exactly at the point that the vents are completely closed. It's a tiny detail but I like the neatness of it.
A little clearer perhaps to see what I'm trying to do. 
In reality it's just a piece of 3mm thick strip with multiple cuts in it so that you can .. ... ...
... ... 'Lazy man' bend it into a flared arc so that it fits ... ... ...
... ... on the inside of the main door just below the top inner edge, it's to 'flick' the smoke away from the top door gap. It really seems to work a treat, I've seen alot of these type of stoves billow smoke from the top edge no matter how tight the top edge fits.
And then lazy man style weld up the gaps. Again you'll probably find the heat from the welding has distorted your nicely fitting door again, as before a little gentle (snigger) attention from a (dirty great) hammer will sort it nicely.
Now for the catches ... ... ...
Now for a little ingenuity, you'll need to source some small steel tube that fits over an easily sourced bolt. I use M10 bolts, but anything around that will prob work as long as the tubing is a fairly good sliding fit (eg: slips over and doesn't bind or rattle).
Cut the bolts short so that you can infill the end of the bolt to the nut to stop movement
Again the tube should be free to turn around the thread but not bind or rattle.
Now weld them to the doors, weld the ashpan door turret on first. As I said earlier 'the devil is in the details', weld the lower turret on so that one flat side of the bolt head forms an end stop for the sliding plate at the point where the vents are fully open. If you've done it right then the vent door will stop perfectly at fully open and fully closed positions. A nice touch huh? Bah humbug to the lot of you, I like it anyway :P
I weld a short bolt onto the door vent to act as a handle, somewhere around midpoint will do.
Now for the latch itself, it's a little inelegant but it works. Chop a few pieces of square bar ... ...
Tack the shorter pieces onto the tube at a perpendicular (erm, like a right angle, but it sounds less fancy).
Lazy man style bend n' weld the catch but TAKE NOTE, the longer arm needs to lean slightly away, they shouldn't be parallel.
Tack them to the bottle body, you can just see that the upper arm leans slightly out from the bottle. You need this to happen, it's pretty critical, as the latch arm swings down it will tighten the door against the body.
When you're sure it's all relatively inline then burn the welds in properly.
I weld a tab onto each door in order to stop the latch swinging all the way around when open, again it's just a detail but I like it.
I think you can see what l was aiming at.
So at this stage you should have something like .. ...
Now to the chimney and top valve (yes it goes on, you can't escape yet, I have Yet more to say).
Pilot drill holes for the jigsaw and chop a smoke hole,
Clean off the paint for welding,
and really burn in the weld. It's going to be a major stress point so really wind up the welder to get good penetration.
Chop a hole in the back of the tube, this is for the top damper/butterfly and to make it easy to clean the chimney.
Now drill a clearance hole (for your standard bolt size) through the piece that was cut out, somewhere around mid-center.
And then cut out of thin sheet an ellipse (elongated circle) whose narrowest dia in the inside dia of your tube. It'll make sense in a minute, trust me. Ah, ... ... then again maybe that's a bad idea ... ... snigger.
Pop a bolt through the hole and slide on a slightly shorter piece of your tubing, l always put a washer under the bolt head, it seems to lessen any binding.
And bat abit of weld on to hold them together.
Tack the disc on to the rotating shaft and check it will both fit into the chimney and work as a butterfly choke. A little 'attention' with an angle grinder usually sorts out any issues.
When the butterfly is in the fully open/upright position weld on a strip inline to it. It's a convention thing, when the arm is inline with the tube you now know that the valve is also inline and fully open.
Drop the assembly into place. What I do here is weld on tabs to mark the fully open and fully closed positions for the butterfly valve (just like what was done for the bottom vent). You never know what kind of muppet is going to use the stove you've made so I try to make mine relatively idiot proof with touches like this. And before anyone says that idiots are constantly evolving l know already, I frequently out smart(dumb?) myself.
Using strips of steel from various cut-offs you've already made, weld on overlapping strips to make the assembly fit against the body of the chimney.
With a small amount of fire cement on the lips it should form a nice gas tight seal, as well as being an excellent overall limiter it is also (as the butterfly is fixed to the hatch) suited for cleaning.
Now cut n drill two 'Tabs' with a clearance hole big enough for your bolt threads, a couple of spacers (I used a few bar offcuts).
And simply weld the tabs n spacers on the removable plate and weld the bolts onto the chimney. Nice n simple :) or should I just say simples? Squeak :))
Burn your welds in and hey presto, here if you look closely I've added an arrow pointing up, it's a little more idiot proofing.
That's the chimney done, now for a few more last touches. Only a few and then I'm done, honest.
I like to make an ashpan with a removable handle, it's really really easy and finishes off the whole thing nicely.
Ideally the ashpan should be as big as you can make it so that it still fits and is easily removable, before you go cutting it out of steel just make a mock up out of card. It's cheaper to bollocks it up and take a little longer than make out of steel and have to throw it away. Trust me on this, I've still got a few earlier attempts lurking around under the bench hiding in shame, meh.
Before you fold up the sides, roll the edges. Just do the first bend over the side of your block/anvil to about 90Degrees.
Then coming in at about 45Degrees hammer the outer edge, because the steel will have work hardened on the right angle bend it will want to roll further up, let it. Then hammer on the edge at 90Degrees to complete the simple rolled edge.
You should end up with ... ...
Now fold up the sides ... ...
... fold over the tabs, and then weld. By now you should have a nice rigid ashpan.
For the removable handle I use a cheap wooden handled chisel from a local pound shop (cheap mass produced stuff). Chop off the blade after it narrows ... ...
... .... weld a hollow tube over the end ... ...
... and then weld on a small piece of offcut. One simple but effective handle.
You might have to open up the rolled edge slightly for the offcut to hook into, and you're done.
Now the most satisfying bit, the first firing. I tell everyone it's just to burn the paint off, however, that's not entirely true. It's mostly for the smug satisfaction of sitting by a brand new gas bottle stove which I made. Once she's going well you will begin to hear the flame roaring and the wood crackling and popping. It's a fantastic sound. I hope you get this far, try it, and then tell me how smug you feel. Go on, I dare you. Just let me know, ok?
Well you made it to the end of this instructable, so now go make one. If a muppet like me can make what I (and others) think is a rather decent little stove through trial and error, then it's not beyond the realms of possibility that with all the above info that so can you.
As a side note, there is no need to be limited to the little 13kg bottles. I made this beast from a slightly shortened large bottle.
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