Above the roof , mount and , Aim a Winegard HD7698P antenna with a Winegard AP8275 preamp at about 225 degree magnetic compass.
Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
Here are some antenna mounts ,
http://www.ronard.com/909911.html ,
http://www.ronard.com/34424560.html ,
http://www.ronard.com/ychim.html ,
http://www.ronard.com.
Buy the ronard antenna mounts at solidsignal by typing the word ronard in the solidsignal search box.
Here are places to buy antennas and etc. ,
http://www.solidsignal.com ,
http://www.winegarddirect.com ,
http://www.amazon.com.
If more/stronger signal strength is required then with the antenna mounted above the roof then here is a way to get the antenna higher ,
http://www.ronard.com/Tripods%200703/4712.html ,
http://www.palcoelectronics.com/pe300.aspx.