By this paper it is aimed to reveal low energy design strategies of building schemes which are still at an early stage of the building design process. The study has two main steps; one is to reveal the impact of design parameters on building performance and to identify which parameters are the most effective ones. Sensitivity analysis method is used for evaluation of the effective parameters. Three representative school building schemes have been modelled and the input parameters are determined. The analysis has been carried out from point of view of annual energy consumption. The latter step is to propose a guideline. The outcomes of the first step are used to develop a list of energy efficiency design recommendations for two extreme climatic region of Turkiye. The expected consequence of proposed guideline is to make aware of designers on the importance of early design decisions for future performance of building design in the main climatic regions of Turkiye.