It is made of plywood, a few 2 x 6's, and a lot of plumbing parts. The folding design is great for storage, and in my case, the catapult actually went up on the roof of a church for the main launching event. It fit up a ladder through a roof hatch with no trouble. (Well, other than the fact that it is bulky and heavy).
The counterweight is two 60 pound bags of concrete, which gave about a 100:1 ratio for the pie pumpkins and basketballs. After the pictures were taken I also added several bungee cords (2 x 18" and 2 x 24") to assist with pulling the weight down, and it added another 20 feet or so to overall distance.
Just something fun about catapults!