Dear Lakshmi garu,
1. Buying a Flat in Gram Panchayat/ Town / City, it does not matter. Basically you have to see whether the title of the land is perfect or not.
2. Whether the permission obtained for the Gram Panchayat, in which you have to verify the number of Floors sanctioned, number of Flats Sanction and total Sq.ft/Sq.mts sanctioned for each floor to avoid deviation in construction of Flat. you can consider upto 5% of unauthorised constructed area not beyond that.