The importance of a reliable cost estimate in the various phases of building projects is beyond dispute. However, in the traditional context, preparing a detailed cost estimates requires extensive worker-hours. Consequently, it is not feasible to be performed repetitively. Considering this, cost estimates are performed during the design phases and the bidding process, leaving gaps were project cost can grow out of control. This paper presents an integrated cost budgeting and cost estimating model for building projects. By integrating multiple cost databases with Building Information Modeling (BIM) geometrical data, the proposed model streamlines the process of cost estimation. The generated estimate complies with AACE International class 1 / class 2 classifications. It is also capable of rendering cost estimates in multiple work breakdown structures, allowing it to be implemented at both the design and construction phases (e.g., UniFormat™ is assembly-based for the design phases, and MasterFormat™ is trade-based for the bidding and construction phases).