When building terrain, look for solid materials that are light weight yet solid at the same time. Styrofoam, cork board, and foamboard are sturdy, yet solid. You can use thin pieces of plywood too, but these are known to simetimes bend and warp in large pieces. plan ahead for yout project, choosing whatever you feel will do best. Cork is good because it is solid, easy to cut, light weight, and resistant to fluids used during painting. You want your terrain piece to be attractive yet easy to carry and store. I generally like to carry and store my terrain in left over paper boxes that I get from work. So if I was making everything out of heavy materials, I'd have a heck of a time carrying all that stuff around. Basic pieces of scenery to start with are hills of various shapes and sizes, templates for forests, and rough terrain templates.
