A Rough Guide
As a general rule of thumb, 1 kW of solar capacity typically requires around 80–100 sq. ft. of shadow-free roof area, though this varies with panel wattage and layout.
What Else Matters
Actual layout depends on module dimensions, roof orientation, shading from nearby structures or trees, roof geometry, mandatory setbacks and the mounting structure used.
A site survey is the most reliable way to confirm exactly how much capacity your roof can accommodate.