How to Construct a Gable Roof

Measure the length and width of the area over which you will build the roof. Add 24 inches to the length to get the length of your ridge beam. Cut the 1-by-10 inch board to this length. If your roof is too long for a single board, use two.

Determine the pitch of your roof. The pitch indicates the number of inches of vertical drop over a span of 12 horizontal inches. For example, a roof that descends 6 vertical inches is called a 6/12 roof.

Cut the angles on the ends of the 2-by-6's to conform to the pitch of the roof. For example, for a 12/12 roof, cut the ends to 45 degrees. Cut the rafters to a length that will overhang the eaves by 12 inches. Find the angle using a framing square and lining up the numbers of the framing square on the edges of the rafters to make the correct angle.

Hold the ridge beam up in the air. You will need several assistants to complete this step. With the ridge beam in the air and the wide flat side perpendicular to the ceiling below, position two of the rafters so they extend from opposite sides of one gable end up the ridge beam. The ridge beam extends beyond where the rafters meet it by 12 inches on each end. Nail these rafters into the top of the wall below and into the ridge beam with the tops of the rafters flush with the top of the ridge board. Do the same at the other end of the building. You now have a ridge beam supported by two rafters at each end.

Install the rest of the rafters by nailing them in at 16 inch intervals between the two pairs of rafters that you installed at the ends of the building. Cut bird's mouths, which are right-angle cuts, in the bottoms of the rafters to fit over the tops of the walls.