ST & TDS on construction contracts

Hi friends,

I have a doubt on construction contracts. When a contractor receives a payment for the work, both ST & TDS is deducted. Can u plz tell what is amount on which both of these are deducted. I think first ST is calculated on the total bill amount and then TDS is deducted on the remaining amount. Can u plz confirm preferably wid the help of an example.

Thanks in advance
Swati