Use this calculator to estimate the area of your roof and cost. The “House Base Area” is the area of the land the house covers. When measuring, be sure to include the eaves covered areas. If the house is irregular in shape, you can divide the house covered area into a few simple shapes and add their area together. The roof pitch defines the steepness of the roof. It can be measured or can be estimated via by comparing your roof with the roof pitch image below.