To build it I am using 12" square (for walls, $1.60/sq.ft) , 6" square (for floors, $5/sq.ft), and 1"x2" mosaic (for stairs, $10/sq.ft) slate tiles and DAP brand silicone. All purchased from Home Depot. I also ended up buying a 7" tile saw for $90. If I had the saw earlier I could have cut all the slate myself and saved a few $$$. Below are some of the pieces marked for cutting and being test fit. Sections from each floor of the tower have to be cut out so the stair become functional and the axolotls can swim between levels.