Check your local building code to determine how far the hearth must extend in front of the firebox and the area on the sides and top of the opening that require noncombustible material. Expect 8 to 12 inches on the top and sides and a minimum of 18 inches for the hearth. When it comes to the hearth, the deeper, the better. There's nothing worse than a hot ember that burns a hole in the carpet. The remainder of the wall can be any material you want, from drywall to plaster to the rustic appearance of wood. More