A useful roof assessment combines an energy estimate with a physical survey. A sunny map cannot tell you whether a roof is structurally suitable.
Start with what surrounds you
Note trees, nearby buildings, chimneys and roof features that cast shadows. Shading changes during the day and across seasons. Photograph the roof from safe ground-level positions; leave access and structural assessment to a competent professional.
Ask for roof-specific estimates
The European Commission’s PVGIS tool can help estimate solar production for a location and orientation. Use it as a starting point, not a substitute for an installation survey. Ask your installer to explain assumptions about shade, system losses and the area available for panels.
Coordinate with future work
A roof likely to need major repairs soon deserves attention before equipment is fitted. Ask whether access, scaffolding, waterproofing and future removal are covered. Also identify who will check any local permission requirements before a contract is finalised.