Gst on constructed commercial office space

GST is applicable on under construction properties but not on completed, ready-to-move-in apartments. If it is under construction then you will have to pay tax as charged by the builder @ 18%. ITC will not be available as per section 17(5).

As per the clause 5(b) of the Schedule II of CGST, Act,
2017, construction of a flat / house / complex intended for sale
is a supply of service. & GST is applicable

However, if the entire consideration towards the
Flat/House/complex is received after the receipt of
completion/occupancy certificate from the competent authority or
after its first occupation, whichever is earlier, then such
activity is neither a supply goods nor a supply of Service, as
provided under Clause 5 of Schedule-III of CGST Act, 2017.
Accordingly, a transaction involving sale of such immovable
property after initial occupation or after receipt of occupancy
certificate, is a sale of immovable property and it does not
attract GST.