Record the weather and timing
Note when the moisture appeared, whether it followed prolonged rain, wind-driven rain or another event, and whether it stops when the weather changes. Photograph internal staining and the relevant exterior area from ground level if safe.
Map the inside location to the roof
Record the room, wall or ceiling area and its relationship to ridges, valleys, gables and chimneys. This gives the thatcher or surveyor a better starting point.
Bring forward previous work
If the area has been repaired before, attach the earlier photographs, invoice and contractor note. A recurring problem is much easier to investigate with history.
Track the professional finding
Record what the competent professional concluded, what work was recommended and what was completed. Do not turn an unconfirmed suspicion into a permanent statement of cause.
Keep emergency work distinct from final repair
Temporary protection or emergency patching should be logged as temporary. When permanent work is completed, close the action with new evidence.
Source guidance can change. Check the current version and obtain property-specific advice where needed.