Sheet metal roofing can prove to be a durable and long lasting material that is available in several different styles and shapes. While sheet metal is an option applicable for just about any roofing situation, every roof will require a different amount of material. Estimating the amount and cost of sheet metal roofing is usually an easy enough task that requires only basic tools.
Things You'll Need
 Tape measure
 Calculator
 Pencil
 Paper

Measure the length (side to side) and width (ridge to eave) of a roof surface using your tape measure. If the measurements have an inch remainder (such as 5 feet 8 inches), round to the next highest whole number.

Divide the length of the roof. Using the calculator, divide by the unit width of the sheet metal you are going to use (most commonly 2 feet) to calculate the number of metal sheets you will need to span the roof length. For hip roofs, measure only one triangular section and calculate it as one rectangular section, as you can divide its amount between the two triangular ends for the roof face.

Divide the width of the roof by the unit length of the sheet metal you are going to use (this is most commonly 8, 10, 12 or 20 feet) to calculate the amount of metal sheets you will need to span the roof width.

Multiply the the number of sheets from Step 2 by the amount from Step 3 to find the total number of sheets needed for the roof face.

Repeat Steps 1 through 4 on the rest of the roof faces to be covered with sheet metal roofing, then add together to find the total number of metal sheets you will need for the roof.

Call your local building supply store to quote the current cost (per sheet) of the metal you will be using. Multiply this unit cost by the total amount of sheets you calculated in Step 5 to find the total cost of sheet metal.
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References
 Estimating in Building Construction; Frank R. Dagostino and Leslie Feigenbaum; 2002