off ofna forums:

Believe it or not building jumps is really an art. Plywood is not the best medium for a jump. Generally accepted thought is about 37degrees is about the ideal angle for the face of a good jump that gives best lift and most distance. Also the approach is critical. You don't want the approach to be a sharp angle, like a flat board on a flat surface. A sharp sudden angle at the lip of the jump is horrid. You need the lip to gently curve from the ground to the slope so that the suspension doesn't have to compress suddenly. Otherwise it's more like hitting a slanted wall at high speed. The front shocks compress untill the nose bottoms out and then the shocks unload bouncing the nose skyward. Also if you are going for really long high jumps you defenately want a second ramp to land on. Contrary to what most folks like to think, landing an 8-10lb buggy or truck from a 10-12 foot jump at 40mph is not good for them. You need a downside ramp to land on.

http://www.freeramps.com/

http://www.heckler.com/ramps/