Do you have a copy of the basic rule book yet? The 'clash of warlords' scenario at the back has a list of basic terrain pieces and recommended sizes (up to 20x20 cm for small pieces or 30x30 cm for large ones). I'm planning to build my terrain based on that list, so 3 woods, 1 section of rocky ground, etc.
I'll probably add a river/stream and a few extra buildings as well to allow me to play river crossing and village raid type scenarios.