If the layout is to be moved and stored, I suggest the track plan be flat. You'll find grades and overpasses make moving and storage harder. Of course, they also are harder to build and keep the track joints smooth.
I would also guard against too complex of a layout. You can easily make certain areas hard to reach to marshal the cars, and maintenance can become a pain. The complicated "spaghetti bowl" type layout often requires tighter than necessary curves and short straights to fit "as much as possible" on the layout. To many people try to jam as much in a space as they can, and the results are disappointing, creating a situation that makes racing on it frustrating rather than challenging.
I think you'll find the hollow core door small enough to begin with, so make a layout with the widest radius curves possible and longest straights that you can. It will still be a small track no matter what you do, but less aggravating to race on and maintain.
Stumpy in Ahia :character-oldtimer: