Every kind of roof needs some sort of frame to provide support and to attach it to the walls of the structure it covers. Metal roofs, which are made of overlapping corrugated metal panels, typically have wooden frames. A metal roof is highly durable, making it an appealing choice for sheds and other practical structures. Metal roofing is also an option for homes and garages when their design accommodates metal's modern, industrial appearance. Building a frame for a metal roof involves determining the roof's weight and installing enough structural lumber to support it for the life of the roof.
Measure the span of the walls of the building over which you want to build a metal roof. Calculate and note the length and width of the roof opening. If the building has walls of different heights built for use of a single-slope roof design, then also note the pitch, or angle, of the proposed roof line
Enter into a roof-framing calculator your data from Step 1 as well as the metal roofing material's weight per square foot. Roof-framing calculators are available online. Indicate the type of framing you plan to build based on the kind of building. For example, a roof for a detached garage may require full trusses while a small roof for a shed probably will be a single-slope roof with a frame made of joists. Write down the results from the roof-framing calculator.
Mark pieces of pressure-treated, 2-by-6-inch lumber to the sizes indicated by the roof-framing calculator's results. Label each measured and marked piece to indicate its position or number in the framing project. Use the calculator's results to determine how many joists or trusses to mark on lumber.
Lay the first piece of lumber that you want to cut across a pair of sawhorses, and cut the lumber to the marked size with a circular saw. Repeat the procedure to cut each piece of lumber.
Assemble trusses on the ground using truss ties and 1-inch long galvanized nails. To do so, either insert each piece of lumber into the opening of a truss tie and nail through the pre-drilled holes or lay pieces of lumber so they abut one another, lay a truss tie across their seam and nail the truss tie into place.
Set a ladder so you can climb it to reach the top of the building's walls. Measure and mark the locations where trusses or joists will be attached to the wall frames. Use the roof-framing calculator's results as a guide.
Nail truss ties into place around the rim of the roof opening by using 3-inch long galvanized nails. Either attach truss ties at the locations you marked in Step 6, or place one truss tie at the site of each vertical wall stud for a single-slope roof.
Raise the trusses or joists into position from the ladder or by using a hoist and one or more helpers. Attach the trusses or joists to the truss ties with 3-inch long galvanized nails.