FYI, I just had a friend who is a cabinet builder strongly suggest that I build this out of something other than MDF. He says MDF has no span-strength. He says its good on compression-strength, so it'll hold the bike up fine, but he worries about the top piece will bow and break. Also that the tie-down holes on the front piece will eventually snap right off at the corners.
Finally he reminded me that MDF is not great with humidity and would be real bad with standing fluids on the floor soaking up into the support pieces and destroying it.
I'm gonna use it for now, since its built. The first project going up there is a scooter, so I'm not worried about weight. But if you decide to build this, go w/ some plywood, not MDF or particle board.