What aspects must I evaluate before purchasing a flat in Sector 89 Gurgaon?

[reeltor estate]

I am in the process of buying my first flat and would like to know what I must check during my visits. Should I pay attention to layout, construction, ventilation, parking, maintenance, or location when I am checking out the available Flats for Sale in Sector 89 Gurgaon? Also, I would like to know how much everything will cost me before booking one.