Step 1
Measure the angle for the edge of the roof with a protractor or compass. Measure the rafter height 6 to 8 inches from the edge of the roof.
Step 2
Transfer the measurements to a piece of 2-by-6 lumber. Cut a notched piece with the circular saw, matching it to the end of the rafter. This notched piece is called a "lookout." Repeat this step for the number of rafters along the roof line.
Step 3
Position each lookout on the inside or outside ends of each rafter. Secure each lookout to a rafter with the nail gun.
Step 4
Attach a 1-by-2 fascia strip along the outer edge of the lookout. Place a second 1-by-2 fascia strip along the same line on the rafters. This will complete the frame for the box gutter.
Step 5
Place a sheet of tin coated steel inside of the framing for the gutter lining. Bend the tin coated metal to form the shape of the gutter.