This one is super easy to make - http://www.taiwancamping.net/2009/10/heineken-wood-gasifier-stove-downdraft.html
But- his hole arrangement is all wrong. VERY IMPORTANT!!- buy a unibit! It's absolutely essential to making clean round holes in thin metal. Unless you are ok with the, "I made this in 5 mins wtih a pair of pliers and a screwdriver look", then disregard my previous statement.
In the heinekin can- drill 10 or so 1/2" holes around the bottom perimiter. Drill the bottom of the inner can as shown in the instructions, but DO NOT punch any holes around the sides of the can at the bottom. then, drill many (32 maybe?) 3/8" holes, about 1/2" - 1" down from the top, on the sides of the inner can. You can't possibly have too much secondary air (at least as far as I can tell from all of my testing).
And his pot stand in those instructions won't last long. It needs to be ti or steel to withstand the temps. I have mine made from .012" thick stainless steel and they glow red when it's burning nicely.
I don't have any construction pics online, but here's a shot of mine burning at its best - https://lh3.googleusercontent.com/-tPfTHyJVuFk/TWlOtiPnumI/AAAAAAAAAXs/OZjCWG3Bg_c/DSC06090_email.jpg
Here's a shot of it burning more normally - https://lh5.googleusercontent.com/-aMqrcx_ij-8/TWlOsybgZfI/AAAAAAAAAXs/YfQDMlg-JzU/DSC06085_email.jpg
This is without the diffuser disk - https://lh5.googleusercontent.com/-DVP6M1W8D8E/TWlOsPC3y2I/AAAAAAAAAXs/Cx3lJvaVFps/DSC06077_email.jpg
There are two fundamental problems with these compact backpacking wood gas stove- heat loss and poor mixing of fresh air and fuel. My little diffuser disk makes a small bot noticeable improvement by forcing the wood gas outwards to where the fresh air holes come in, and by also slowing down the convection and reflecting some of the heat back down into the combustion chamber. Ideally, you'd want more of the combustion to occur down inside the stove, not 3" above it, and have the rising hot gasses heat your pot. The bottom of your pot is very cold and strips heat from the combustion process, causing smoke, soot, and tar to condense onto the bottom of the pot.
Well worth the read if you are interested in this subject.