structures gunna be built with 2x4's, it will have extra supports in the middle, and the surface will be two 1/4" pieces of 4' by 8' ply wood, which should provide the strenght of a 1/2" piece of plywood, and the flexibility of a 1/4" piece.
Will leave the jump in the lake for a few nights and days, then in the sun for a few more, and hopefully the wood will warp to its final shape...
If all works out, I'll post pics of the results

 dude i cant wait to ride this!

 5 feet ? how longs this f*cker gunna take to build ?