For my layout I have 2X4 framing, covered with 5/8” 4’x8’ plywood and then covered with 2” x 4’x8’ sheets of cheap white bead board(Home Depot)
All my basic landforms are made with this material. Just a Hot glue gun, sharp Utility knife and add some details.
I have just really started to detail my layout lately. Here are some pics
Al