How to Figure Tin for a Roof

Sketch a simple two-dimensional drawing of your roof.

Section the sketch into rectangles and triangles so that you can find the area of each part of the roof.

Measure your roof by climbing a ladder with a tape measure. Measure the length and width of each rectangle in your sketch, as well as the base and height of each triangle in your sketch. Write these measurements in the appropriate area on the sketch.

Calculate the area of each shape on the sketch of the roof. To determine the area of rectangles, multiply the width times the length. To determine the area of triangular sections, multiply the base times the height and divide by 2. For example, if you have a rectangular portion of the roof that measures 50 feet by 20 feet, multiply 50 times 20 to get an area of 1,000 square feet for that section. If you have a triangular section with a base of 10 feet and a height of 30 feet, multiply 30 times 10 to get 300, then divide by 2 to get an area of 150 square feet for that section.

Add the areas of each shape in the sketch to find the total area of the roof in square feet. For example, if you have two rectangles with an area of 1,000 square feet each and two triangles with an area of 150 square feet each, add these figures to get a total area of 2,300 square feet. This means that you will need at least 2,300 square feet of tin to cover your roof.

Add 10 percent to the total area to account for waste. In this example, 10 percent of 2,300 is 230. Add 230 to 2,300 to get 2,530 square feet of tin.