Your roof is 544 square feet.
Square footage is area expressed in square feet. The way to calculate a rectangular area is by measuring the length and width of your area then multiplying those two numbers together to get the area in feet squared (ft²).
If you have on odd shaped area, such as an L-shape, split it into square or rectangular sections and treat them as two separate areas.
Calculate the area of each section then add them together for your total. If your measurements are in different units, say feet and inches, you can first convert those values to feet, then multiply them together to get the square footage of the area.
To learn more, go to www.calculatorsoup.com.
There are also many online square footage calculators that you can utilize to make your calculations easier:
Redbeacon.com - Square Footage Calculator
SquareFootage.org - Square Footage Calculator
Calculator.net - Square Footage Calculator
BHG.com - Square Footage Calculator