Despite all the available solar technologies and the opportunity to reduce energy demand, solar energy systems are in most cases not used in buildings today. The lack of technical knowledge among architects is one of the main barriers according to the IEA-Task 41 entitled Solar Energy and Architecture [1]. In fact, several problems face architects during the design and set-up of buildings that integrate PV systems, for example, the complexity and uncertainty of estimating the PV performance. To overcome this problem and to examine these opportunities, this study developed a decision tool to guide architects to size PV systems during early design stages. The aim of the study was to help give architects a generic idea of the potential of PV as an energy source and how to integrate PV in the building architecture. The tool is based on a transient simulation database built using TRNSYS16 and underlies research considering PV technology parameters and local climatic conditions of Egypt. Simulations of three PV systems are compared with measured data in order to form a basis for optimal design and prediction of PV system performance. For this tool we developed and presented simple graphical visualization of the verified performance indices. For example, yearly maximum output energy of PV modules, for different inclinations and orientations for Aswan, Alexandria and Cairo. The overall benefit of this simple decision tool is informing and assisting architects and designers in order to increase the use of solar energy in buildings ; Peer reviewed