Suppose there is a house size 9×12 m. Do not forget that the roof should have cornice overhangs, so the length of the lower sides of the slopes will be greater than the length of the walls of the house. Therefore, in our calculations, we will increase these indicators by half a meter from each side. Accordingly, they will amount to 10 (from the side of the triangles) and 13 m (from the trapezoid). Suppose that the length of the ridge beam is 5 m — this will be the size of the second base of the trapezoid. Let the height of our trapezoid be 4 m. So, we find out its area: we add up the lengths of the base — 13 and 5 m, divide by 2 and multiply by height. As a result, we get 31 m2 — the area of one of the trapezoids. Since in our calculations the cosine of inclination is important — for example, it is 0.87 (from 30 °), then we multiply the resulting area by this number and round. As a result, we get 26 m2.
