A while ago, someone posted an instructable on a Halloween pneumatic which "popped" out of a toxic waste can. I wanted to build it, but I didn't have any of the equipment and I'm somewhat frugal so I set out to see if I would be able to replicate it with items that I already had around the house.
Step 1: Build your based for piping in compressed air
I used 3/4 and 1/2 inch pvc pipe. I just eyeballed the sizes, although I wanted all the pieced together to fit onto a piece of plywood which would then fit into the bottom of a trash can. So you might start with measuring the bottom of your can (or box or whatever to see how large or small you need to make it.
As I said, I used items around the house - so I had a water hose splicer,
Step 2: Connect Pieces to build base.
As you can see, I used the 3/4 T with the 1/2 inch connector as the center. I extended each end about 5-6 inches just to stabilize the base (I anchored it down with 3/4 pipe hangers - shown later).
Step 3: Build your pneumatic cylinder.
This was the really easy part for me. I just needed to know how much I wanted my prop to be lifted up and cut a piece of 3/4 inch pipe just about that length. This will house your piston and eventually connected to the base I build earlier.