Leaning a piece of plywood on a milk crate is good and all, but as I am an adult with health insurance, a computer and access to CNC equipment, I want to make a solid launch that won't recreate the scene from Napoleon Dynamite.
I used Tinkercad to create a simple wedge ramp model that fit to particular dimensions that I wanted. I'm only a little redneck, so my jump is only going to be around 9" high.
Then you can take the model into 123D Make to create a cross-sectioned model that will glue together and be really really sturdy.
3'x4' 1/8" masonite board
Step 1: Draw it in Tinkercad.
Now you have a solid model of your ramp. You can take it to 123D Make by downloading from Tinkercad
Under the Design menu, click Download for 3D Printing and save the file as an STL on your computer.