http://www.axialracing.com/ftp/rockcourse/

http://www.youtube.com/watch?v=gWeeOchcM4M

If you can combine the foam wood method and the video of the real rock course you will be in good shape...

When I was in TN we went to a private gun club, that a lot of the members were apparently into r/c crawling, and they had a nice track, it was completly round, with a foot print of about 15x20', and you stood in the middle, to get in there was a part of the track that was about 6 1/2' tall where the truck was over your head {that part was just like a bridge, with 2x3's planked so you could see under your truck when looking up... The rest was made with the foam all cut up and airbrushed to look like rocks... There was mirrors on all the walls around it so you could see both sides of your truck, it was pretty impressive, I wish I took pictures....
Good luck, I hear the most important part is having a few trucks of different scales there to test it as you build it...
Also they use some loose tires to make tire grooves and tire traps, that add some difficulty to the course...