Accurate assessment of effort, time and resources for estimation of project cost is a challenging task for project managers. Several methodologies are commonly practiced around the globe for project cost estimation based on the project's scope, type, and availability of resources. In developing countries like Pakistan most of the construction projects face delay and cost overrun, and construction industry continues to use traditional methodologies for preparation of project cost estimates. Present study developed a probabilistic framework for project cost estimation using Monte Carlo Simulation. A probabilistic model is proposed for estimation of total project cost using data on key risk factors that included (1) labour efficiencies, (2) machine efficiencies, (3) construction material wastages, and (4) construction items' prices. Using data from completed highway projects, model validation results revealed that developed model has the ability to predict reliable future project cost.