The construction industry is considered an essential element to stabilize countries economically. In the UAE, this sector has received a lot of attention and development since the discovery of oil. This has enhanced the continuous expansion in construction activities. Recently, the construction projects in the UAE and KSA together reached around 70% of the whole projects in the Middle East region, and the majority of it was in Dubai, which in 2018 enhanced its Gross Domestic Product (GDP) to reach 14.5%. Therefore, the decision-makers apply multiple methods at different projects in order to achieve the prime factors for project success which are: cost, time, quality, and safety. However, the construction industry exposed to different variables and unpredictable causes, such as availability of the main resources, different environmental conditions, financial issues, and poor productivity. Meanwhile, there is a great interest in delivering residential construction projects to cover the demand of shelter on time and within the estimated cost limits, and most importantly with the required quality, considering all variables. The aim of this research is to define and rank the factors that contribute to the cost and time overrun on the construction projects. The authors defined the most frequent factors that were affecting the project's cost and time from literature review, then applied the Relative Importance Index (RII) technique on 7-point Likert-scale results that were conducted by the participants. They were thirty construction project managers in the UAE, whose experience range between 5 and 20 years. The most significant factor that contribute to cost overrun is “delay in material delivery.” On the other hand, the most significant factors that contribute to time overrun are “the inadequate experience of contractor” and “delay in material delivery” as well.