>>10881556What you could do potentially is start off with a module system like T-Trak and start yourself with a basic setup. Once you wanna go bigger you could just make more modules or integrate the modules into a permanent layout.
Alternatively, make a standard 4'x8'/3'x6'/whatever and leave some interchanges going off the layout that you could expand upon at a later date, kinda like this layout where the bit on the left is an entirely separate layout that connects to the main layout via a branchline.