This is a ruin that I made of cheap styrofoam. This was relatively easy to make and took me about one hour thirty minutes to make. It does look pretty realistic.
Although this was primarily a ww2 war-game ruin, it can be used in Warhammer. So how I made it was I took the styrofoam out of a box and used my fingers to break off some of the wall, so it looked like it was ruined, then I used my knife to cut some chunks out. I used light brown and white for the outside, and dark brown with white, or green for the interior. For the floor I used black and white, with watery light brown.