You can get 5x10 plywood, cost aint cheap though.
Someone laminted mine top for fun, pressed with 2x4 cribwork and a pickup truck on top. Wouldnt take a dime; wanted the wood gone.
You can barely fit 027, O, and Super O together on 48 inches, so Im sorry but I caved in, 4.5x9. I wanted a FEW inches for scenery.
....., but wanted a siding more,,.. and then a platform too. Then I built up. An el.
The reach is the best reason to build small. Mobility another. It may also eventually be moved and become part of something larger. I see my " little" layout as a module. Id like a group of them, each in different stand alone themes, all interconnected by two main lines.