Those look great for height, and I'm sure the manufacturers of your cars are rubbing their hands together with glee at the prospect of selling more parts.

I built mine out of a 4x8 sheet of plywood and some 2x3's. One side is 4' long, the other is 3'. Height at its peak is 21". It's hinged in the center, so I can fold it up and lean it up against the wall in the garage. Two lengths of chain hold it up when laid out. I'm going for distance (about 12' with my 'Pede on 7 cells).
The reason for the different lengths is that there's a steeper angle on the 3' side. I can't hit that side as fast though.
I almost wish I had built it somewhat curved, for a smoother transition, but... meh.