This research aims to identify and investigate factors affecting productivity in building construction sites. The importance of these factors has been studied extensively through a widely spread questionnaire among 183 participants. The research covers the MENA region, especially Egypt and Saudi Arabia as the main markets there and diversity of mega construction projects. The comparison of factors importance will help in making right investment decisions and better understanding of the nature of building construction sites, as well as it applies to a boarder construction environment as most of working construction companies there are international. Among all factors affecting productivity, 49 factors were carefully selected throughout carrying out extensive search and factor frequency of similar researches, they were categorised into seven groups. The survey was utilised for data gathering from Egyptian and Saudi construction sites. This research also provides simple and comprehensive recommendations and suggested method of determining loss in productivity that can be adopted by construction managers for an effective management of construction sites and higher productivity.