if it is fully constructed ie sale after obtaining Completion certificate then it is sale of immovable property and hence no GST as it is covered under Schedule III.
After 1st April 2019 as per new scheme commercial property in Residential projects ( commercial space carpet area is less than 15% of total carper area) is taxed at only 5%. If it is in project other than Residential Project ( ie carpet area of commercial space is more than 15% of total carpet area) it is taxed at 12%. Incase of ongoing project it will depend on the option exercised. If sold after obtaining completion certificate there will be no GST