Flat roofs present a large potential of suitable areas for installation of PV (photovoltaic) plants. Flat roof PV installations have the advantage of being able to be optimally positioned with support structures, and the inclination angle can be adjusted. Due to the important technological development existing in the PV sector, there are different PV technologies in the market, whose energy and economic features substantially differ. This paper describes some useful parameters to assess the technology and distribution of modules to be installed in flat roofs and terraces of buildings. The effect on the energy parameters of the modules tilt and disposition is analyzed in a case study, considering different technologies. (C) 2010 Elsevier Ltd. All rights reserved.