The next consideration should be the distance from the future dish location to where the satellite receiver will be located. As the distance increases so does the amount of cabling needed between the two points. The more cable you have the more it costs. More importantly as the distance increases the amount of signal to the receiver decreases. Also be sure the dish and any cable routing will be entirely on property you own or lease.
Terrestial interference is also a concern for satellite downlink points.
Interference can come from telephone company microwave links, cellular phone towers and even airport radar sites. Roof locations for a dish installation are not uncommon but present unique concerns. These include access to the dish location, ability to properly anchor the dish mount, and terrestrial interference that may not be a concern at a ground level location. Your first decision is between a solid or mesh dish design. Solid dishes offer many advantages over a mesh dish and should be the choice for nearly every situation.