I only have 3.5 x 4 foot space, so I made a train board for under the tree and that board hangs in the garage in the off season.
Last year it had Marx O-34 on the inner loop and S gauge on the outer loop. This year the S gauge outer loop will be replaced by an O-42 loop of O-27 profile track made by K-Line.
The plan is to run 6 inch Marx and maybe some 3/16 scale Marx, and a bit of 3/16 scale prewar American Flyer.