Take your choice. Personallt the 30 degree initial angle is faster for takeoffs than the other one. Either will work fine though using 2" square steel tubing as supports. You might want to also consider placing a board or rolled angle along the edge to keep the cars from rolling off the side.
Steel is going to get heavy so you will need to get some kind of devise to move this around. Palet Jack? See if someone in your pack has availability of one.
I hope to complete the ramps this weekend. I was hoping for last weekend, but I ran into a couple issues. Anyway, I will post some pictures when complete.
I will also post some pics of the race day events.
I do have more pictures if anyone is interested.
Here is a picture of the latch for the starting gate I fabbed;