The solar chimney power plant (SCPP) is a promising solution to produce electrical power from solar energy. The optimization of the solar setup geometry is required to enhance its performance. In this paper, a numerical study is presented to evaluate the performance of the solar chimney power plants while varying the collector roof angle. The considered system is defined by the collector height equal to h = 50 mm, the chimney diameter equal to d =160 mm, the collector diameter equal to D = 2750 mm and the chimney height equal to H = 3000 mm. Four collector roof angles, equal to (beta = -1.5 degrees,beta= -1 degrees,beta= 0 degrees and beta =1 degrees, were investigated. For each collector roof angle, the distribution of the magnitude velocity, the air temperature, the pressure, the incident radiation and the turbulence characteristics were presented and discussed. The efficient choice of the optimal geometry is based on the calculation of the maximum value of the air velocity within the SCPP. Results indicate that a negative collector-roof positively increases the air velocity. The obtained results present an interesting data which can provide the thermal characteristics of the air flow for the designers and the engineers to improve the overall efficiency of the solar setup. (C) 2017 Elsevier B.V. All rights reserved.