Leaky roof?

I have a two family brick building in Chicago with a flat roof that slants down towards the rear of the building. The two apartments have virtually the same layout and at the front of the building are sunrooms. That section of the building has it's own small pitched roof, slightly lower than the flat roof covering the rest of the building. My tenants live on the second floor and I noticed the other day that there is bubbling paint on one ceiling in one room and above one window in another room. Both are at the front of the building, where the main flat roof begins. They both occur on or near exterior wall but are on opposite sides of the building (approximately 20 feet apart). Realizing this is extremely difficult to diagnose without seeing the problem, I'd still like opinions about what needs to be done. The roof is about 7 years old. I'm not sure if the entire roof will need to be replaced or just patched. Or if another layer would be put on. I suppose calling a roofer in would be the best bet, but I was wondering if anyone could tell me what I should look for if I climbed up onto the roof and looked around.
Thanks
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It could be bad mortar above the leak on the exterior walls.
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You might check the seams in the coping on top of the paraphet..also what type roof is it? Like built up, rubber, roll etc...could debris causing damming.

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