Any roofer can tell you that whenever you have a protrusion in the roof, you have the potential for leaks. This includes skylights, which in this case break the concrete tile pattern of the roof. Skylights are lined with flashing beneath the tiles to help keep the water out of your home. Like any material, overtime the flashing may break down, or maybe the caulking that seals the flashing has worked its way loose in the freeze/thaw cycle. Usually all that is required to fix this is to reseal or recaulk the flashing.
Skylights can make a beautiful addition to many homes, letting in light and air to rooms that might not receive these things otherwise. Be sure to maintain, repair, and replace as necessary to help ensure that they continue to function just as they were designed to.
