In the winter, a buildup of ice on the edge of the roof can prevent melting snow from flowing into the gutters. As a result the water seeps into the roof. In other seasons, rainwater seeps under damaged shingles.
Notify your landlord immediately of a leak in your apartment roof in order to minimize damage to the apartment and your possessions. Roofing professionals can repair the damaged materials and determine ways to prevent future leaks.
Review your lease and your renter's insurance to determine what rights and responsibilities you and the landlord may have regarding repair or replacement of any damaged personal items and regarding any time you were unable to use the apartment due to the leak.