At Which level of project floor area method is used as pre contract cost control? How cost analysis is done at this stage?

The Floor Cost area method is used at the pre construction stage of any project.

Basically the floor area (Builtup area) for your substructure and superstructure including the working spaces like staircase and ramps are calculated and it is to be multiplied with the current unit rate of construction per square meter. To this is added the cost of preliminary constructions cost , Over head and profits and contingencies to determine the project cost.