In general this will not be a problem. The roof of the building will absorb large amounts of the RF energy. Typically a roof would be expected to decrease signal strength by a factor of 5 to 10 (or more for a reinforced concrete or metal roof). In addition, the FCC requires RF radiation evaluations of high-power rooftop transmitters. Even a worst-case calculation predicts that power density on the floor below an antenna will meet all current RF safety guidelines, and actual measurements in top-floor apartments and corridors confirm the power density is far below all current RF safety guidelines.