What you'll need to build a gun of any sort, whether it's this one or any other is four simple components.
1: A barrel- Without this critical piece, your gun is just going to spit air everywhere and you'll have no place to put a projectile.
2: A projectile- This flies out of the barrel and at your target. This can be just about anything that fits down the tube.
3: A propellant- This forces the projectile out. For this, we'll use air. Compressed air, to be more precise.
4: A frame- Without a frame, your gun is more a mess of pipe that looks like you threw it together in 10 minutes. You don't want that. It's great when in a pinch and you want to try it out, but not so great after a month of battling and/or target shooting when people start asking, "When are you going to finish that?"
Now, in my case, I had the first 3. I felt I wanted a frame that was different. Now, I say this because I appreciate originality, and if you want to build my rifle from pictures alone, feel free, but I wouldn't mind seeing other rifles (I call any gun with a stock that, just fyi) based on my design. Heck, build one just using my instructable as a guide if you want.
Things you'll need:
A barrel in the size of the projectile you intend to shoot and adapters to fit the blowgun.
An air-type blowgun. I found an odd one in someone's garage sale and picked it up for $3.50.
A handful of handsaws (or a few good power ones. I can't make a lot of noise or the neighbors complain)
Plenty of your favorite drink. I chose Mountain Dew and good ol' Black Coffee.
A piece of wood. any dimension works, and any type (pine, oak, spruce, maple, etc) will work. Just remember that you'll have to deal with the lovely factors of more sweat in the project if you use harder woods.
Your most comfortable pair of safety goggles/glasses. You need your eyes for this project, so protect them.
Plastic and metal plumbing parts. I used metal for the gun, and plastic works, too, if you want to lighten it.
A regulator (probably the most expensive part of my project and the one that I actually had to buy.) You need this to take the air pressure down from tank pressure and make it variable. This is a nice factor to have.
Quick Connect couplings (optional) for those of us who don't want to waste any time after we finish shooting. Nothing better than a quick connector to disconnect the gun from your air tank.
An air tank. Where else will you... well, I suppose you could pump it up with a bike pump, but I didn't like that. I prefer an airtank in the backpack, and a small electric compressor to fill the tank at times.
A marking device for making rough measurements (that's what I did, at least)
A dremel (or other brand of rotary tool). This will save your butt many times. Ours has been beaten and abused, but still works.
A work surface
a) 2 part Epoxy (the stuff I almost swear can't have been made by mortal hands.) You'll need this to make your rifle frame bond to the barrel and the rest of it.
b) Electrical tape and superglue to hold the barrel together.
c) Extra zipties for holding the barrel together.
Zipties to hold everything together.
Teflon tape for sealing airline connections.
Wood screws to hold things together.
A screwdriver to install wood screws.
A drill might help at times. Sometimes a Dremel, while it spins faster, can't do the job.