When I was younger,I was about 12 years old and my first layout I ever builted was 3 feet by 6 feet,and was rolling in under my bed when I was'nt play woth my trains.I was get some foldable leg under it to get it at the right height to play..
It was made of 15 inches Atlas track sections,that still availiable today by Atlas,it was an oval with a siding,that was curving at 12 inches raduis and deserving 3 branches,when I got older and built a bigger on,I bring the small layout to my cousin's place and I taked the subway to get to his place with the layout..
if you have a bed that let rooming under it,it can make a great thing,by making the frame and add small wheels under it(you can take wheels from a computer chair,very easy to put in) ,you have just to roll it from under the bed to play,and roll back under when finishing to play,and it do not take any place in the room when stored..just need to spare some space beside the bed to be able to play.and having foldable legs under it to be able to get it at the right height you need to play.