Using Project Contract how to do costing in Project costing

 We are implimenting project contracts and doing the shipping,revenue and invoice generation through the project contracts.We are not able to attach the cost of inventory to the Project Costing module.

We are initiating the revenue and billing events through the project contracts.Can you please assit how we can attach the cost to the project.PAB is the workaround. Who can we attach the cost directly to the project costing module through the inventory module

Please advise