If you own or are buying the house then here is the Federal Law that says Yes you can install a antenna on the roof.
http://www.fcc.gov/mb/facts/otard.html. If you are renting or leasing and the owners agrees to roof top placement , then you can put the antenna on the roof. The best place is at the High point of the roof. Here are two more antenna mounts ,
http://www.ronard.com/34424560.html ,
http://www.ronard.com/ychim.html.
http://www.ronard.com