Sides are .75” plywood. It was a bit warped, that's not all that important for this use. The back wall and front entrance wall are half inch. Again leftovers from another project and somewhat warped. Used table saw to cut the pieces. When I built my first cat shelters I used a handsaw and a jig saw to cut the pieces. It takes longer but it works. To make the holes for the entrance and the windows I used a drill to make a hole in the 4 corners, and a jigsaw to cut between the holes.