Noida Ext: Usable space vs. brochure claims

Is the carpet area difference between Buildcon Maghad Mansion and Mahagun Marvella really that significant, or just brochure talk? I'm fed up of renting and checking both. Marvella is ready but pricey. Maghad Mansion looks cheaper, but what about the actual usable space after all the deductions? Builder trust is also a big concern, honestly.