Work contract

My querry is If  'A' company has given contract to 'B' for setting up a tower. 'B' further divide the same contract under two contracts one for erection commissioning of tower and another for supply of parts required in construction of tower and issue separate invoices for both of them. But 'A' condition is very clear that if 'B' fails to erecte tower his second contract of supply of parts will also be cancelled. In other words both contracts are abide on each other.  Now if we take this under Work contract services what will be taxable value whether the value of erection contract portion will be only taken or both the contract of erction and supply will be clubbed and then service tax will be charged. As the single contract was bifercrated into two but now value of sale of goods and services are showing seprately.