The digital broadcast Tv stations/channels are Very Strong at your location. The perfered antenna on the roof is a Winegard HD7000R antenna (that is designed to receive All the broadcast Tv channels of VHF low band 2 thru 6 , VHF high band 7 thru 13 and UHF 14 thru 51) aimed at about 155 degree magnetic compass. The HD7000R antennas receiving elements at the back of the antenna are 8 feet wide. And that is 100% Ok. The situation is that people will be on the roof as time goes along , and sooner or later someone will break off the long metal reception elements. That being the case , install a smaller ANT751 antenna aimed at about 155 degree magnetic compass. Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html. There are antenna mounts that are Made For mounting a dish and Tv antenna on the same mount. The antenna will use the same ground as as the dish. If your dish coax cables are Separate from the other coax cables of the other people that live in the building then it will be easy to connect the antenna to the dishes coax cables. The Tv transmissions are Very Strong at your location , I do not think that a antenna amplifier will be required. The Tv Must Scan for the Digital Broadcast Tv Channels sometimes named the 'Antenna Channels' or 'Air Channels' because the Broadcast Tv Transmissions travel through the air from the transmitting antenna to your receiving antenna. Do Not scan for cable tv channels or satellite Tv channels. It will be best if the installation is done by some one that has some idea of what to do. Here are places to buy antennas and etc. ,
http://www.winegarddirect.com ,
http://www.solidsignal.com ,
http://www.amazon.com.