Roof area is not living area
A two-story house does not have a roof equal to all its living space. Porches, garages, overhangs, slope, and different roof sections change the measured surface. A roofer measures the assembly being covered rather than applying a household square-foot number blindly.
The calculator supports 1,500 to 3,500 square feet of roof surface using a $4 to $6 planning input. You can keep the 2,000-square-foot example, enter a known surface area, or use a known footprint and pitch. The result clarifies a budget band; it does not diagnose repair needs.