Noida carpet area: the real sqft story

Did a site visit to Victory Ace last weekend, and also checked out Imperia The Sephyra online. Fed up of renting, finally taking the plunge, but this carpet area thing is confusing. Builders advertise super built-up, but the actual usable space seems way less. Victory Ace feels more efficient, but I'm not sure. Is Imperia's carpet area better for rental potential? Also, builder trust factor is huge for me. Any experiences with Imperia or Victory Ace delivery? What's the real sqft you get?