4. Frame the walls for a 12x16-foot building, leaving a 4x12 front porch. Build the walls using 2"x4"x92 5/8" precut studs at 24 inches on center. Build each side wall 15 feet 10 1/2 inches long to leave room for a front cripple to support the porch beams. The front and rear walls will be 11 feet 5 inches to fit between the side walls. Use pressure-treated 2"x4" boards for the bottom plates.