I'm planning on building a track in my backyard tomorrow. The room my dad will let me use gives me enough for 4 wide lanes beside each other about 40m long. Does anyone have any ideas for a layout and construction techniques? My friends and I usually bash and have 1/10th and 1/18th mostly basher vehicles. Will I need anything but time, wheelbarrow, shovel, drainage tile, and skidsteer?

Edit: This is my plan, any suggestions or altercations are welcome.