Originally Posted by M3AG
Wood of course (2 x 10 with 3/4" floor plywood). Untested? well maybe not as a car ramp but been used in constructions for sure.
A friend helped with calculations and max load is about 4500lb (Center load) per 7"x 7" and about 8000lb (Uniform load) with sag factor of 0.01 inch. Now that's per wheel! If for any reason the top layer fail to hold the load the lower sub frame can hold up to 20000lb per 7" x 7".
That should work - hopefully you have a lot of storage space. Should add wheel stop blocks at the end.