My tools used were a cordless drill with a 3/8" (10mm) bit and a pair of diagonal wire cutters. Before I began, I coated all of the foam in PVA glue and a liberal dusting of sand. I also coated the upper floors to add some texture. I also used many pieces of cut up sprue to fill in the gaps where it might not be obvious that models were not supposed to be placed in that spot. I took some pieces of sprue and used them to brace the upper floors. Although the for sale sign was good thick plastic, it still flexed enough to concern me. I used super glue to hold the sprue in place. In the below view you can see the post added to support both levels. A wire rope with knots was added for decoration.
You can see how the walls not have jagged edges and there are holes from shells drilled though the walls. The amount of destruction is really a matter of taste, as long as your ruin can fit models easily and it's easy to tell if you are supposed to be able to see the models inside the ruin. In the below image, you can see I removed a good section of the right corner on the second level to increase visibility.
I contoured the foam at the rear entrance with a drum sanding attachment on my drill. I made sure to make two depressions like the tracks would leave after many entries and exits.
I made a ladder out of some craft sticks I had. I feel it's nice to show how the models will get into a ruin and since the first/ground level is blocked on this side, a ladder was the obvious choice. In my mind, this ruin has been occupied many times and a previous resident left the ladder behind.
After I was finished with the damage it was off to painting. I primed the whole ruin flat black and then drybrushed the entire thing with a gray craft paint. I had to remove my predator sponsons to get it to fit easily, but it is non-standard. Some might blame the ladder on the right or the pole on the left. I just say if it doesn't fit, it can't get in.
I had a great time building this. Please let me know what you think of this building and what you think would be a great rules-compliant, usability-focused, terrain project.