To install a gable roof, first hammer in the top plates to the outside walls, and then install the ceiling joist onto the top plate. For the ceiling lumber, cut and measure the material from 2-by-4s. Form the peak of the roof by using the ridge board, which should use 2-by-6 lumber.
Keep something to stand on while assembling the roof by laying planks across the ceiling joists, which you later move to the outside of the roof. Measure the height of the gable roof by using the Pythagorean theorem to measure the roof’s slope and the length of the rafter boards.
Attach the rafters to the ridge board at 16- to 24-inch intervals. The height of the roof and the extension of the wall should guide you in the measuring of the appropriate length of the rafters. For each pair of the rafters, make a collar tie. Attach this to the rafter boards to strengthen the roof from the inside.
Put the gable roof together, and tighten the top plates of the wall into the notches in the rafter. Nail planks to the rafters, and use mitered planks to cover the ends of the gable roof. Use tar paper to nail the planks, and then put on asphalt shingles and roofing nails. Offset the rows of the edges of the shingles to center them.