Service tax on flat

Hi,

I request for some clarificartion on the proposed service tax on my new flat, which is not yet registered.

Let the Total cost be Rs 'X'

I have already paid Rs 'Y' to builder at various time before march 2010.

I request your help in below queries

1. What will be the service tax that i have to pay if i register the flat now?

2. Is there any benefit if I register the flat before may 1st?. My builder told me tax will be in effect from the date the finance bill be passed in parliment. Is it true or will it be from april 1st?

3. Do I have to pay service tax on total amount or the remaining amount that I am going to pay now ( Rs X - Y ) as I have paid the rest before March?

4. Do I have to consider the total cost X or the cost which will be shown in the registration?

Thanks in advance,
JK