Here's a track I made several years ago for Mini-Zs. All the walls are padded and covered with vinyl, and it can be configured for either oval or roadcourse. I since ran out of space to store the track and ended up selling it, but it was fun while it lasted.

Road course:


Oval:


I also made a portable track for 1/10th sedans that gets pretty regular use. It's basically just white boards that join together with simple hinges - it works pretty well. I'll post some pictures of that soon.