Generator sets can be placed just about anywhere however environmental factors should be considered. 

Altitude and lower temperatures can influence fuel supply characteristics.  Heat and direct sunlight can create over heating for engines and other vital components which make up a generator set. 

Salt which is present near the ocean or simply evaporation or condensation associated with normal structure equipment can destroy generator set enclosures which can be just as expensive as the working parts of a generator. 

Adequate space for necessary ventilation or clearances off structure or other equipment should be considered. 

Erosion does occur over time, so attention to surrounding areas and drainage should be considerations for placement.  If there is slope associated for the location of the generator, retaining walls should be considered.

Especially for units utilizing air cooled engines, adequate clearances around the generator is necessary for cooling the engine.  Failure or oil vaporization are results for inadequate air flow.

Having adequate work space is necessary for service or repair.  Repair cost will be more expensive if removing generator enclosure parts becomes necessary simply to change the oil.

For environments where snow is possible, for gaseous engines, the fuel regulator should be placed high enough or vented so that snow does not effect the regulator's operation.