Sub contract MRP Settings

Hello

Can any one guide me , how to do MRP settings for subcontract Proces.We want the system to generate MRP for the subcontract Process, We need B & C Material to Make A. A is a finished goods , B is going to Produce and ship to subcontract Vendor and C will be Procured and directly shipped to Subcontract Vendor . We are going to get back A as a finished Goods. Can any one please tell me what will be the MRP Settings required to create a Sub contract Purchase Requisition ?

Thanks

JJ