It's not going to sound very good. A bit hollow perhaps...   A bonus: notice the built in shelf where the keys would be. It's the perfect size to place an electric piano keyboard. We can have somebody play it for real. To get the shape of the piano, we took a piece of plywood and placed it on top of one of our real pianos. Then, simply traced it. Its being moved to the theater today. The legs poke through the bottom and actually support the top of the piano.   We're wrapping the piano with wiggle wood. This is a very flexible plywood that comes in 4'x8' sheets. You can get the stuff to bend along fairly tight contours. The sheet is very expensive. Around $50 per sheet.