My hack for comparing true usable space in Gurgaon flats

What's the trick to understanding actual usable space in Gurgaon flats? I'm looking for a manageable 3BHK around Sector 61, maybe ₹2 Cr. Kids have moved out, so a compact place with an elevator is key. Builders like Lion Infra Developers LLP show big super areas, but carpet area feels much smaller. How do you guys compare projects on true usable space, not just super area? And are construction-linked payment plans always better, or does a lump sum get a better deal? Just trying to avoid surprises after selling our old place.