That's what I told my kids when they asked me what the heck I was doing.
This ruined building is made from foamcore with some model railroad ballast for dirt and debris, and the tiles are made from cardstock cut into squares. Actually, the tiles are made from the cardboard separators that they use in cases of liquor to keep the bottles from banging into each other (but let's not judge, shall we?). It's all glued together with wood glue- I prefer to use wood glue for things like this over hot glue because you get a little more time to shift things around if you don't like where you've stuck them. If you use hot glue, you pretty much have to get it right the first time.
I based this off of RubbishInRubbishOut's 'Making simple City Fight terrain' videos. It's a pleasant enough way to kill a few weekend hours.