(a) Disaggregate Approach (Costing Using the Prices of Individual Pay Items or Treatment). In this approach, the overall cost of an entire project is estimated using the engineer’s estimate or the contractor’s bid prices for each specific constituent work activity (also referred to as a pay item) of the project. Pay items may be priced in dollars per length, area, or volume, or weight of finished product, and is often reported separately for materials, labor and supervision, and equipment use. This method of costing is more appropriate for project that have passed the design stage and for which specific quantities of individual pay items are known. It is generally not appropriate for projects whose design details are not yet known.