Construction projects require accurate quantity information for estimating, procurement, and cost planning. Understanding BIM quantity take off helps professionals use digital building models to obtain measurements from modelled elements. This can reduce the need for some manual measurement and make quantities easier to review as the design develops. However, the reliability of the results depends on how accurately the model has been created. Model information still needs to be checked before it is used for commercial decisions.
http://www.uniccm.com/bim-quantity-take-off