GST is not applicable on ready to move in flats as a complete flat is a final product on which GST is already included in its input services and products used for construction.
Although GST is applicable on an under construction flat or apartment. The rate of GST is 5% which is reduced from 12% to reduce the overall cost and promote buying by middle class.
The builder cannot charge GST on the cost of flat but he can charge GST on other charges which is applicable at the time of final payment. For example, builder charges for electrical meter connection, IFMS, external and internal wiring, electricity load, club charges, advance maintenance, etc. There maybe more than the above-mentioned heads of charges claimed by builders from buyers at the time of final possession.
You can check the final breakup of heads on which GST is charged and at what rate. The rate of GET on flat coat will only be 5% which is already inclusive so inky breakup of same will be given, while in other heads of charges the rate of GST will be different and can be 12% or even 18%.
Rate of GST is uniform throughout India so the rate of GST for Hyderabad will also be same as is for any other city.
Before you negotiate with builder, do check the heads of charges in which GST is charged and at what rate.
Live before you leave.