The thermal performance of the building envelope is mainly required for guaranteeing a comfortable and hygienic interior climate. A roof is a part of the building envelope which provides protection from the thermal damage of the sun. To improve this protection ability, we can consider using a ventilated roof, which has a ventilation layer known as a cavity, beneath the roof cover panel. The objective of this study is to evaluate the influence of such factors as the slope of the roof, size or shape of the openings (i.e. inlet or outlet), effective cross section and cavity depth on the improvement of the air flow in the cavity for better thermal performance of the ventilated roof. In this study, the influence on air flow which is caused by the characteristics of these elements is researched. The evaluations are carried out by way of experiments.