Leaks are rarely sudden. Most of them leave breadcrumbs before they become a ceiling stain.
Check the attic before the ceiling
Dark decking, musty air, wet insulation, and nail condensation can appear before interior drywall shows visible staining.
Study penetrations
Plumbing boots, vents, skylights, chimneys, and satellite mounts are common leak suspects because they interrupt the roof plane.
Watch the weather pattern
A leak that only appears during wind or thaw cycles points to a different problem than a leak that happens during every rainfall.