- 1). Find the angle of the roof on your construction plan, or blueprints. Use a protractor with the baseline of the protractor aligned with one face of the roof and the peak of the roof centered in the baseline, on the center mark of the protractor. Read the angle from the protractor where the opposite face of the roof intersects with the angle gauge on the outside of the protractor. Divide this angle by two.
- 2). Measure the rafter length on the plan. Use a scale ruler with the correct scale ratio, as described in the legend of your construction plans. This is typically written as a ratio or fraction. Use the edge of the scale ruler with the same ratio as your plan to determine the actual length of the rafter. Measure from the peak of the roof on the plan drawing to the end of the angle overhanging the wall. Subtract ¾-inch from the overall length of the rafter for one-half the thickness of the ridge beam.
- 3). Set your miter saw to the correct angle. Turn the table of the miter saw by unlocking the handle, either by lifting up on the snap-down handle or twisting the knob on the handle. Turn the table until the indicator is aligned with the correct angle on the miter gauge. Cut one end of a 2-by-4 or 2-by-6, depending on the roof frame, at this angle. Measure and mark the board at the correct length.
- 4). Cut the bottom end of the rafter at the same angle, in the same direction to form an elongated parallelogram. Fit the rafter from the ridge beam to overlap the top of the wall. Attach the rafter to the ridge beam by nailing at an angle into the beam. Use a hurricane tie bracket to attach the rafter to the top of the wall. Use 16d nails to make the attachment, one nail in each hole of the bracket.