How should the water path be traced?
Begin inside with the room, inventory, equipment, or finish affected. A ceiling mark identifies an impact point, not necessarily the roof opening. Move to the roof and compare the interior location with drains, seams, curbs, roof edges, and changes in elevation. Water can travel beneath a membrane or along a deck before it appears indoors. Note recent rain, whether the condition is active, and any earlier repair near the same zone.
Then inspect the roof covering where water could enter. A separated lap, cracked sealant, loose termination, puncture, or open flashing joint points to different work. Check whether the surface around the detail remains sound enough to receive repair material. If a drain is slow, distinguish a blocked bowl from a membrane slope or drain-flange problem. Each observation belongs on a roof plan or photograph so the owner can compare the proposed work with the actual location.