Back in 1976 I started this layout in the sitting area in the Attic.
All the framework was 1 by 2 pine, screwed together, (I was thinking that at some point I would have to move it out). The mountain section was designed to shoehorn into the existing space, the stairs came up in the middle of the area so I built the frame to be 1/4 inch short of the space then put felt pads in the gap to keep things from moving. The layout was supported by legs and not screwed to the wall. That part of the layout ended up being a little over 4 foot wide, nearly 12 foot long, and had a rise of about 10 inches.
The slope up to the second level was actually too much but I convinced myself the it was prototypical as the loco’s could run up and down with one or two cars (just not the whole train). The terrain was mainly created with the classic cardboard/newspaper hard shell, detail pieces were carved into foam then covered with that grey modeling material.
The Yard layout was a simple 4 by 8 sheet with the addition of a triangle corner to allow for the big Union Station. The two pieces connect together in the T shape with loose pin hinges it passes over the stair well and has portable legs to keep it from bouncing as we ran trains.
Now the interesting part is, this whole section disconnects and will fit under the mountain section when guests come and use the room, the gap in where the two connect was covered by a large foam mountain side. In this picture you can see the hinge connector an the semicircle with foam mountainside removed.