Well, what scale vehicles will you be running on the track and how much space in total do you have available?

Lane width usually 8 - 10 ft wide depending on how many cars will be running at the same time.

Jumps are all about angle. You can have a jump that's 4 feet tall but very steep, or a 2 foot tall with a shallow angle. You'll fly further and faster on the 2 foot one compared to the 4 foot one.

Some other ideas for actual shape and stuff can be found in this thread: http://www.rcuniverse.com/forum/m_8792104/tm.htm

Good luck and let us know some more info mate.