My original plan was to build Radstock GW in P4 (the proper one, not the later arrival), I did a lot of research, but finally realised that it was perhaps just too big. Ended up building Clutton.
Layouts I have toyed with are Pensford in 2mm with the viaduct, Tylwych (mid Wales line) in 2mm with the mountains around, Bilson Junction (Forest of Dean) in P4 (lots of wagons!).
Time now against me, so smaller layouts are being built ...