For the majority of antenna styles, the height an antenna can be mounted above ground/sea level is among the most important factors governing the performance of RF equipment. Generally the higher an antenna can be mounted the better it works as issues like terrain and vegetation obstructions can be negated. In remote areas it may be necessary to construct large towers to achieve the required performance. However, where available, existing buildings can be used as pseudo towers.
A simple and cost efficient way to gain height for antennas is to use existing structures and install posts, tripods or guyed masts etc to the roof. There is no standard roof mount design, rather mounts are fabricated to suit particular applications whether that is a single yagi on a residential property a grid array on an industrial compound to sector antenna farms mounted on top of a CBD skyscraper.
Using rooftops to mount RF equipment is such a common practice that many companies (particularly those who provide IT services) make arrangements with landowners of tall buildings or buildings located on hills in the areas that there business operates to pay a monthly fee to 'rent' space on roofs.