For the skirmisher system Mordheim, you need loads of ruined buildings, barricades, rubble, walls etc. My collection is by no means complete, but it is sufficient for normal games. You will realize that there are two types of buildings: Some are GW cardboard buildings that I put on bases to add stability (and for looks of course), others are scratch built from balsa wood, cardboard, plastic sprues and what ever came my way.