How to Build an A-Frame Patio Cover

Measure the width and length of the patio with a tape measure; the width will determine how to cut rafters for the roof, the length will tell how many rafters are needed. Decide on a pitch or slope, the number of inches of rise per foot in the roof, expressed as 12/12, for instance, for a roof that slopes up at 12 inches for every foot of run, which is half the width of the roof or the length each rafter must cover.

Build four exterior walls with top and bottom plates and 4-foot vertical studs of 2-by-4-inch framing lumber. Make a rectangle the length for the wall formed with top and bottom plates and studs at each end. Square the outline by measuring diagonally until those distances are identical, then fill the interior with studs spaced 16 inches apart.

Erect the walls around the patio perimeter and fasten them with concrete nails, into a slab, or use 16d framing nails to attach them to a wooden deck. Use a level to make sure the walls are plumb vertically. Tie them in place by nailing corner studs together and covering the tops with a second cap board, nailed so it overlaps the seam where two walls meet.

Lay a 16-foot 2-by-6-inch rafter board on a flat surface with the 6-inch face up to mark a rafter for a 12/12 pitch. Put the point of a framing square at the bottom of the board, with the thin tongue to the right along the end of the board. Align the 12-inch mark on both the tongue and the wide blade of the square at the top of the board and draw a line with a pencil along the tongue to mark that top or plumb cut for the rafter.

Look up 12-inch mark on the "length of common rafter" table on the square's blade. Multiply that differential, 16.97 or that length for every foot of run, times the run, 8 feet for instance for a 16-foot-wide patio. Measure that length, 135 3/4 inches, down the bottom of the board from the plumb cut. Draw a 1-inch line vertically into the rafter at that point. Draw another line from the top of that line 3 1/2 inches back up the rafter bottom, for a triangular birdsmouth notch.

Add an overhang, at least 18 inches, or more if you want the A-frame roof to hang down farther below the walls. Total those lengths and make another angle mark, like the plumb cut but figuring with the point of the square at the top of the board. Go back to the plumb cut, measure 3/4 inch down and draw an identical line, to allow for a 2-inch ridge board between rafters.

Cut all rafters to that pattern with a circular saw. Set the first pair in place at the back of the roof. Nail them through the birdsmouth to the wall caps with 16d framing nails and a hammer, two nails on the inside of the rafter, one on the outside. Plumb these rafters with a level and brace them temporarily with two-by-fours nailed to the rafters and to stakes in the ground. Let the tops rest loosely together.

Set another pair of rafters at the other end of the roof. Cut a 2-by-8-inch ridge board to the length of the patio roof. Lay out rafter locations on it with a speed square; draw a line across the 8-inch face 1 1/2 inches from the end for the first rafter mark. Measure 23 1/2 inches from the end and draw a second line, for the outside of the second rafter. Draw lines at 24-inch increments based on that line for the length of the roof. Mark both sides of the ridge.

Slide the ridge board in place between the two sets of end rafters; push it up from the bottom. Level it with a level and fasten it with framing nails through the rafters, two nails in each rafter. Add other rafters at the marked locations, nailed to the wall caps and to the ridge board.

Sheath the roof with oriented strand board, add roofing paper and shingles or cover it with translucent vinyl panels or metal roofing, depending on building codes and personal preference.