Not enough ventilation. Moisture from inside the house is condensing on the underneath side of the roof.
Every roof requires regular inspections so repairs can be made before leaks set in. You can inspect your roof without every setting foot on your shingles by using a pair of binoculars. Staying on the ground and using your binoculars, you can inspect the shingles all around your roof. Look for any that are curled, broken or missing completely. The attic should be inspected for leaks. The binoculars and a good flashlight will allow you to see throughout the attic. Watch closely for rust stains on the nails and condensation. Finally, step back and look at the overall roof. Dark stains running down the shingles indicate a loss of the protective granules and could indicate that it's time for a new roof.
attic
The term you might be looking for is Ridge.
sometimes, this answer is obvious: a hole in your roof, missing shingles, leaks, or animal living in your attic. Other times, the signs you need a new roof are little more subtle. if your roof is more than 12-15 years old, it may be time to get a replacement and get ahead of any problems that result from a damaged roof.
The room under the roof is called an "Attic".
That depends on what you are trying to say. Nails are in the roof to hold the shingles in place, but he stands on the roof while nailing those nails.
attic
Other than leaks, you can sometimes see loose or missing shingles from the ground. To be certain about the condition of your roof, a roof check should be done by a professional roofer or house inspector. They will look for loose shingles, missing nails, detached flashing and other issues.
More insulation in the attic, better air flow through the attic, direction the roof is pointing, less sun, the pitch of the roof, Any or all of these.
loft, garret, roof space
Attic.
attic