I personally use 10"x10" solid wood ramps. An 8' length cut on a bias with a chain saw, produced two with about 3' of ramp and 2' of level. Twenty years of service and 8 cars so far.
I would be a little leary of open wood construction.
Edit: Didn't see above post. Looks good, and solid (albeit layered) construction. I just tip mine up and walk them back to garage.
p.s. Nice rear wheels. Thanks for great pics. Stairway to Heaven comes to mind, but hopefully there will be no need for oil changes there.
