Welcome to dakka!
Looking forward to seeing what you've got.(and possibly blatantly copying it

)
Some basic scenery ideas
Hills:*paper-mache over a wire netting base. Hard to carry out but can create natural shapes and is very tough with enough layers
*high density polystyrene. Can be carved out to make it just as natural. A lot weaker than paper-mache when done properly.
Ruins(osgiliath,temples for fantasy etc)
*low density polystyrene. When cut in rectangles,arches,etc and painted and textured properly can look very good and realistic.
Far future ruins
*low density polystyrene. Cut into building like shapes and break in the roof and walls. Not really effective but it is all i know of.
Lakes.
*high density polystyrene. Cut into a crater shape and fill with ready mixed fillern also rippled plasticard is at some gaming stores. This actually works really well as long as the crater is well painted and big.