How to Build an Angled Roof on a Shed

Determine a pitch for the shed roof. Match the house by putting a framing square at the eave and measuring the height from the square to the roof 12 inches in from the edge; a difference of 5 inches, for instance, will be a 5/12 pitch, rising 5 inches per foot from the wall to the peak.

Cut rafters to the proper pitch using a framing square, tape measure, pencil and circular saw. Get the width or span of the shed and divide it by two to calculate the run, or distance each rafter must cover from peak to wall. Divide the shed length by 24 to find the number of rafters, two on each side of the peak, so a 12-foot-long shed needs six pairs of rafters or 12 rafters total.

Lay a 2-by-4-inch rafter board on a flat surface with the 4-inch face up. Set the point or heel of the framing square at the bottom of one end. Align the pitch mark on the thin tongue, 5 inches for a 5/12 roof for instance, and the 12-inch mark on the wide blade at the top of the board. Draw a pencil line on the angle on the outside of the tongue; this is the plumb or top cut for the rafter, to form the peak.

Look up the "length of common rafter" table on the blade and find the figure under the pitch mark, 13 under the 5-inch mark, for example, or 13 inches for every foot of run. Multiply that differential times the run; for an 8-foot-wide shed, the run would be four, making a rafter length from peak to wall of 52 inches.

Measure that distance down the bottom of the board and draw a vertical line 1 inch into the board. Measure 3 1/2 inches back up the board and connect that point to the top of the vertical line, forming a triangle called a birdsmouth to fit on top of the shed wall cap. Add any desired overhang from the end of the birdsmouth, typically a foot, and cut another angle, like the plumb cut but reversed by putting the heel of the square at the top of the board.

Go back to the plumb cut and draw an identical angled line 3/4 inch into the rafter to allow for a peak ridge board. Use a circular saw to cut all those angles, then use that rafter as a pattern to cut all other rafters.

Set one pair of rafters in place at the back of the shed, plumb them with a level and brace them with 2-by-4s nailed to the rafters and to stakes in the ground. Fasten each rafter to the wall caps with a hammer and 16d framing nails with the birdsmouth firmly on the wall cap. Put two nails on one side of the rafter, one on the other. Let the rafter tops rest against each other.

Move to the other end of the shed and install another set of rafters the same way. Mark a 2-by-6-inch ridge board for the rafters; draw a line 1 1/2 inches in from each end of the board, 23 1/4 inches in from the back end for the outside of a second rafter and 24-inch spaces based on that line to the other end of the board.

Set the ridge board between the end rafters and slide it up from the bottom into place. Level it and nail the end rafters to it with two 16d nails through each rafter. Raise the other rafters and fasten them the same way, working in pairs.

Cover the rafters with oriented strand board decking, with 4-by-8-foot panels running lengthwise of the shed. Overlap the panels at the peak, so one panel edge goes over the edge of the abutting panel. Use a circular saw to trim the OSB as needed. Install roofing paper and shingles or other roofing, like metal panels, as desired.