Use half logs (about 2" in Diameter and width of the shelf), sand the flat half and leave the round half alone, that will be the shelf. Use two more 1.5" to 2" logs for the sides of the shelf flat side on the inside. Assemble it with screws. Then mount it to the wall. I'd show you the one I made for my CDs but I knocked it off the wall and broke it... with a baseball.