Start low soaking the area just above where the leak appears in the house.
How repair a roof leak.
For example soak the downhill side of a chimney first then each side then the top on both sides.
Lift the damaged shingle with one hand and push the sheet metal flashing up underneath the shingle so the sheet metal covers the hole.
Repair leak in roof tips.
Patch the nail or screw holes by slipping a piece of roof flashing underneath the shingle.
If a leak is difficult to find enlist a helper and go up on the roof with a garden hose.
Run water on the outside with a hose.
Isolate areas when you run the hose.
Quickly fix a roof leak by slipping a sheet metal flashing up under the course above the hole.
Have one person climb on the roof and spray water above the suspected leak location.
Look above the ceiling leak point and scan the sheathing leading towards the peak of the roof.
It will give you many signs in your ceiling and the walls that the roof is leaking.
For loose or damaged shingles remove them by pulling the nail out and scraping glue from underneath the shingles before replacing with new ones.
You can hire a professional company for the repair of the roof.
You have to identify the signs and repair them in time.
It may not be a direct line but it will always be above the ceiling leak location.