[Doug G]

I second what Mr_D said about the plywood quality... we built ours with 1/2" ply from Home depot and covered it with 1/16" lexan and after some moderate use and testing the areas between the rib supports is definitely caving in. If I had to due it over (and might still need to) I would use 3/4" ply on the top or a lot more rib supports.

Also be prepared to attach some surgical tubing, springs, or weights underneath the bridge to get the balance just right.