Write an article based on this "Fasten the nailer to the side of your existing building where you will attach the upper end of your rafters. Lay out the rafter spacing on the upper and lower nailers. Determine the roof pitch by stringing a line from the top rafter attaching point to the bottom one. Cut 1 end of the rafters at the angle given to you by the speed square. Nail the rafters against the top nailers. Space the lower end of your rafters on the layout marks and toenail them into place."
To attach a wooden nailer to a metal-sided building, use a self-drilling screw with sufficient threads to hold the nailer tightly. If possible, nail through the siding into the building's framing members. Regardless of what method you choose to attach this member, make sure it is fastened securely. This is critical because the nailer it will support the weight of the roofing, the framing and the person performing the installation. Starting at 1 end, measure the span you determined to use when you designed the building, and mark each space. Marking the edge of the rafter rather than its center will make the mark more visible when you position the rafter. Hold a speed square (also known as a rafter square) plumb against the top nailer where your string is fastened.  Read the angle on the square's angle scale. Test the cut by holding the rafter in position. If the cut does not fit tightly, adjust it. A good fit will increase the hold of your nails when you attach the rafters. When you have established the best angle for the top cut of your rafters, cut each one using that angle. Unless you are certain both nailers are exactly parallel, do not cut the lower end of the rafter. This can be done after the rafters are installed, if cutting them is necessary. For best results, use metal brackets attached to a ledger board. Alternatively, use the toenail nailing method.  Use a pencil to mark the position where you want your boards to join at a right angle. Place the rafter about 1/4" (6 mm) in front of the nailer. Place the nail about 1/2" from the connection point and nail it in straight into the rafter. The key to toenailing is to drive the nail in straight and then at an angle. Tap the nail into the wood about 1/4" (6 mm). Pull the nail up at about a 50-degree angle. Drive the nail in until it protrudes slightly from the rafter. Reposition the board to ensure that the angle is exact. Finish driving your nail through the rafter and into the nailer. Avoid starting the nails too close to the end of the board, as this may split it, and make a strong connection impossible. If this is unavoidable, pre-drill the hole at the correct angle first. Use as many nails as possible without splitting the rafter, especially if you are not planning to use a structural anchor like a hurricane clip to supplement the nail's holding ability.