To measure a roof, start by drawing a simple diagram of its shape from above, breaking it into rectangles and triangles. Use a long tape measure to get the length and width of each flat section on the ground if possible, or climb up with caution to measure along the eaves and ridges. For steep roofs, measure from inside the attic using the rafter length and multiply by the overhang. Record every dimension carefully, then calculate square footage by multiplying length by width for each section a… how to measure a roof 11