Real negotiation limits in Gurgaon new projects

Sector 24 keeps coming up every time I shortlist something for investment. I'm based in Dubai, so can't do a site inspection easily, relying on community insights. With new projects, especially from builders like Aviana Green Estates, how much can one realistically negotiate on price? They quoted a 3BHK around ₹2.1 Cr. Is there a typical percentage off that's achievable, or is it mostly fixed now? Also, for an NRI investor, is a construction-linked payment plan truly smarter than a larger down payment? Worried about total cost of acquisition and managing stage payments from afar.