At Toys r Us I found kids skate ramps made of thick nylon or somthing. They came in a to pack with a conection peace idont use for 60$. works very well and is very storg.
make sure to use plywood
if you make it out of plywood and 2x4s it'll be pretty heavy and hard to carry because of the shape. just one thing to think about.
Thats what she said.
i use cardboard boxes.