Need help

Q: I have recently booked an under construction property, only the first slab is completed.I booked this property by paying the builder 20% of my flat cost, also I paid him the service tax at 3.09% and VAT at 1% on this amount (i.e. 20% of the flat cost)Now he is asking me to pay the remaining 80% of the service tax and VAT in advance (i.e. on the full agreement value) and says that this is required for getting the stamp duty & registration done.Please guide if I should pay the entire service tax and vat amount in advance or should it be paid to the builder in parts as per the completion of the project and as per the bank disbursing the amount on completion of each slabTotal Property Cost - 4027500
Paid - 805500
Remainder will be paid by the Bank on completion of each slab

Service Tax Paid - 24889.95 (On the amount paid to the builder)
VAT Paid - 8055 (On the amount paid to the builder)
Completion of Project - 1st Slab
Total Floors - 7
Locality - Mira Road

Stamp Duty Registration not done, Builder is asking me to give the remaining ST and VAT on the entire agreement value before the Stamp Duty & Registration is done i.e.
Service Tax - 99560
VAT - 32220
Whereas I understand that Service Tax and VAT will be paid on the amount disbursed by the bank at the completion of each stage of construction.