Flat roofs, even the new generation with single membrane coverings need periodic maintenance and inspection.
One of the biggest drawbacks of flat roofs is drainage, or lack of drainage. Although flat roofs do have a slight slope to drain water, they are not nearly as efficient as a pitched roof. Rainwater tends to remain on flat roofs and form puddles, which can lead to material damage and possible roof leaks.
Go up there, remove any debris like leaves and twigs, look for cracking, bubbling or blistered areas. Check around vent, flashings, drains, parapets and any roof-mounted equipment. If you are unable to get to the roof, hire a home inspector or roofing contractor to do an annual inspection. It could save you a bundle.
(Photo courtesy of Google)