Urban wind energy exploitation is an important topic for smart sustainable cities. The present investigation is a step in this direction, considering the latest advances in building aerodynamics, identifying and analyzing the optimum building-roof shape for the urban wind energy exploitation. This investigation focusses in two aspects: the isolated building shape optimization and the analysis of this building in an urban environment. The optimization includes an analysis of the roof-wall transition geometry by testing different variations of a spherical roof, a roof-width sensitivity analysis of the optimum geometry and an exploration of the building aspect ratio effect on the flow. A comparison of velocity, turbulent kinetic energy and turbulence intensity is carried out. The wind turbine positioning on the roof is analyzed in detail. An exactly spherical roof connected to a cylindrical wall is identified as the most advantageous option. Additionally, the effect of the neighboring buildings is investigated considering different heights for the surroundings. The wind flow on the roof is strongly affected by the presence of surrounding buildings, increasing the turbulence intensity close to the roof surface. Slender shapes are identified as the most interesting building shapes for wind energy exploitation, leading to a higher speed-up and to a lower turbulence intensity. (C) 2015 Elsevier Ltd. All rights reserved.