Jes' delightful little pizza inspired me to explore what might be accomplished in a slightly larger space. The layout depicts a 7 1/4" park railway in Gn9. The layout size is 600x1200 mm (2 x 4ft) which happens to be the standard size of foam insulation slabs here in Sweden.
The neat thing about modeling a miniature railway like this is that you can mix anything that will run on 9 mm gauge: Illustrated are a pair of Steve Bennett's Tiny/Tichy and Gn9 stock, as well as a 1/4 scale live steam Porter saddle tank with approriate stock (i e some old HOn30 or OO9 stock, with a riding tender added behind the loco for the driver).
Not much switching taking place: The storage building and siding can house four trains which take turns running around the park..
I would probably finish the left and rear edges of the layout with a tall garden wall, and you could add a rural or even city backdrop behind the wall.