carpet area or saleable area makes no difference to builder community. They will quote carpet area in agreement but will hike psf rate to account for loading percentage.
in the end they make the money they want to
I totally agree with you on this one. However the only thing is that you will know what you have paid for and the builders cant turn back on the actual final carpet area, whereas if super built up is always quoted, the carpet area can change slightly at the time of agreement.