Is it permissible to pray on the upper floors (second and third) of a building constructed on a cemetery?

If the building is independent and there are no graves in the prayer area, then the prayer is valid on any floor of the building. However, if the graves are on the same floor where one prays, then the prayer is invalid, due to the Prophet's (peace be upon him) prohibition of taking graves as places of worship. If the graves are around the building but the land of the building itself is clear and contains no graves, then the prayer is valid. But if the land of the building is part of a cemetery and was usurped, then prayer is absolutely invalid in it, and the building must be removed.