I'm working with a project that comprehends various buildings (~20), from which only 10 will be certified. The complexity of the project is related to the demolition activities that will take place prior to construction. 

Basically, the area in which the new buildings will be constructed was previously occupied by buildings that will be demolished. Not necessarily they occupy the same area.

My question is:

If we try to achieve Option 2, how can we determine the amount of waste that we can generate? Which sq.ft we can use? It doesn't make sense to use the building floor area for the new construction. Would it be the whole area occupied by the demolished buildings? Or the area in which the new buildings will be constructed?