A Quonset roof refers to a semi or halfcircle shaped roof and derives its name from the "Quonset hut" developed as an easily moved, easily assembled utility building for the military. A Quonset roof is typically a halfround shape of any length that can support or accommodate a cathedral or domed interior ceiling structure. To get an accurate measurement of a Quonset roof to estimate the area for new roofing or paint, the procedure requires only a tape measure and calculator.
Things You'll Need
 Cloth or flexible steel tape measure
 Calculator
Mathematical Method

Measure the horizontal width of the Quonset roof to determine the diameter. Measure from the base at each side across either end.

Multiply the diameter dimension time 3.14, referred to as "pi," and then divide the result by 2 to determine the circumference measurement of the Quonset roof.

Measure the overall horizontal length of the Quonset roof and multiply this dimension times the circumference determined in Step 2 to define the area of the Quonset roof in square feet.
DirectMeasure Method

Extend a cloth or flexible metal tape over the outside diameter of the Quonset roof and measure the dimension between the base of the curve on each side. This measurement will define Quonset roof's circumference dimension.

Measure the overall horizontal length of the Quonset roof.

Multiply the dimension determined in Step 1 times the length dimension defined in Step 2 to calculate the area of the Quonset roof in square feet.