For a outside roof top antenna I recommend a Winegard HD7000R antenna aimed at about 45 degree magnetic compass. Here are antenna mounts ,
http://www.ronard.com/909911.html ,
http://www.ronard.com/34424560.html ,
http://www.ronard.com/ychim.html. Also use new RG-6 coax cable on the outside of the building from the antenna toward the Tv. Do not use any splitters for one Tv connection. Every time a split takes place the signal is reduced.