Here’s another couple of pieces I built recently. Both come from a resin terrain kit I purchased 6 or so years ago from Crusader29 (now out of business). This kit has a number of single and double story wall sections that can be combined in a number of ways to create complete or destroyed buildings. I have assembled five buildings from the kit and am showing two here (the other three are sitting on the painting table.)
The first is a two story ruin mounted on Medium Density Fiberboard (MDF). I generally try to put all of my terrain pieces on MDF as it makes them more sturdy and customizable. The floor on the first story is cut up cardboard square, the second is styrene sheeting gridded in 1/4 inch squares available from the hobby shop.
The second piece uses sections that were initially twelve inches long and as high as shown in the picture. I broke the segments up so they would fit on a smaller base. This is roughly nine by six inches. The floor is parakeet gravel available from discount stores.