The inside of the square shelf is 14x14x11, but I recommend that you check the height of any piece of artwork you would like to display and make sure you build the shelf around it. Shelves are 2" thick, made of cabinet-grade plywood and stained. But if a more rustic look is desired, using well-seasoned wood boards may work too, although they will be more prone to warping and humidity levels. Good luck!