ha we have made like 5, they are the most fun thing ever!!!  we made a small like mabye 3 feet long we can shoot off our bikes, and the best one we ever made was about 9 feet long one using compressed air.  we shot a broom out of it and it went about 200 yards to the other side of the neighborhood,  it was hilarious seeing this 4 foot long broom flying like 100 feet up in the air across our neighborhood, it was pretty sweet.   then it blew up one time when we were using it cause we pumped way too much air into it,  it fucked up my friends hand and cut me.  
and there are so many things you can shoot out of it, like flaming towels, any fruit, poop, bb's, water, rocks, sand/dirt. 
the most fun kind we ever made are the hairspray ones, they arent as powerfull as the compressed air ones, but they are so easy and fast to use, you can do like 3 shots a minuite where an air powered one takes like 2 minuites a shot and its way hard to carry around.
its such an awesome feeling knowing what damage you can do from 300 yards away where your not even visible.