Step 1
Start from a fascia piece's left edge and measure 5 1/2 inches to the right. Mark this length near the fascia's top and bottom edge. Draw a line connecting the two marks using a straight edge. Cut along the line with a tin snips.
Step 2
Measure from the bottom of the F-channel (which is the hook piece on the bottom of the rafter face) to the undersill (the top of the rafter face). Subtract 1/8 inch from this measurement.
Step 3
Measure from the 5 1/2-inch piece of fascia's bottom edge up. Place a mark on the fascia indicating the height you measured in Step 2. Move down the fascia's length, placing a few more height marks. Draw a line connecting the height marks with a straight edge. Cut the fascia along the line with a tin snips.
Step 4
Flip the fascia piece over and lay it face down on a flat work surface. Measure 2 3/4 inches over from the fascia's left edge, along the bottom edge and the back side. Mark this measurement on the fascia's bottom edge and draw a straight line down the fascia's back side. This is the center line of the 5 1/2-inch length of fascia.
Step 5
Hold a protractor along the fascia's bottom edge, centered over the mark you made in Step 4. Make a 45-degree line on the left and right sides of the center line using the protractor. The two lines should meet at the mark from Step 4 to form a 90-degree angle.
Step 6
Cut the two 45-degree lines with a tin snips to remove a small piece from the fascia's bottom edge. Hold a metal straight edge along the line you drew in Step 4. Bend the fascia over the metal straight edge until the two cuts you just made meet.
Step 7
Position the fascia corner cap you just made over the rafter face's outside corner. The fascia's bottom edge hooks over the F channel on the bottom of the rafter face. Secure the fascia in place with stainless steel nails.