To build a hip roof, measure the length of the ridge board by subtracting the width of the building from the length. Calculate the length of the rafters by using the roof pitch and the width of the building from the seat cut to ensure there is sufficient contact between the rafter and the wall.
Secure a common rafter with a nail to one side of the ridge board first on one end and then on the other. Nail common rafters on the other side of the ridge board on the opposite side of the others to hold the ridge in place. The ridge is locked into place when the rest of the common rafters are installed, starting from the center of the ridge for balance.
To calculate the length of the hip rafter, start from the corner of the building and go the length of the ridge at a 45-degree angle. Use a framing square for reference, and cut the rafter at a 45-degree angle on the sides that meet the ridge. Attach a string line where the hip meets the ridge to just above the point where the hip meets the wall to keep the hip straight while installing the jack rafters.
Using a rafter table, find the length of the jack rafters. Keep referring to the string line on the hip when nailing the jack rafters into place. Manage and adjust any pressure the jack rafter puts on the hip to prevent warping and bowing. Continue the process on each corner of the building.