Roof mounted solar PV (Photo-Voltaic) systems are as varied in configuration as there are roof styles. Systems can be broken into two basic categories: fixed or adjustable. Fixed systems usually run parallel to your roof and the orientation is based on the slope of your roof and the orientation of your roof peak with respect to the sun. Because the sun is not usually perpendicular to the panels, the panels produce less than the same panels mounted on a tracking system. The advantage of these systems is that they have no moving parts, and there is very little that can go wrong with them.
If you have a flat roof, you can use a single axis roof-top tracker the follows the path of the sun during the day, but doesn’t adjust the tilt to optimize for the location of the sun depending on the season. These are more efficient that a fixed panel system, but less than the dual axis tracking systems.