If the building is not wrapped with metal such as but not limited to metal siding or stucko with stucko WIRE. If the building does not have a metal roof. If the walls are not made of poured concrete. If the building does not have foil backed insulation. If the Tv is not in the basement. Then a SIMPLE NON Amplified indoor Tv antenna will get you most of the channels in green. In any event try a simple indoor Tv antenna FIRST before installing a outdoor roof top Tv antenna
http://forum.tvfool.com/showthread.php?t=233 . . . If you go to a roof top Tv antenna then ANT751 or similar small roof antenna will power 1 or 2 Tv's. . Read and understand this about Real Digital Tv Channels and Virtual Digital Tv Channels and Analog Tv Channels.
http://forum.tvfool.com/showthread.php?t=695 . Here is how to aim Tv antennas
http://www.kyes.com/antenna/poinying/pointing.html . . Indoor or roof top Tv antenna point at about 330 degree magnetic compass.