Vat and service tax

I too have query on Vat and service tax of new flat.

I have booked a flat in Pune on 13-March-12 by paying a initial booking amount. the scheme got completion certificate on 29-mar-12. I did my agreement in month of May-12, which is after getting completion certificate. So in this case will I have to pay the service tax. Initially we {builder and me} were under impression that I dont have to pay any service tax since my agreement is after completion certificate date. But now builder says I have to pay the service tax on complete agreement value.

So please suggest in this case. this seems to be a different case.

thanks,

Sameer