Estimation of cost for building and civil engineering projects with minimum error at the conceptual stage of project development is crucial for planning. This paper evaluated the most significant cost escalation causing factors in building and civil engineering projects. Questionnaires were administered to clients, consultants and contractors to elicit information regarding their opinions with regard to these factors. Mean score value for each factor was determined. Also level of agreement of ranking of such factors between groups was investigated. The results of the analysis show that the most significant causes were the “Fluctuation of price of material” and “Variations” with the highest mean score values of 3.9 and 3.73 respectively. Also there was agreement in the opinions between all the groups with regard to these factors. A linear multiple regression models for the prediction of final cost of construction of building and civil engineering projects were developed using Statistical Package for Social Sciences (SPSS).