Qs regarding issuing Stock to a Project

Hi All, I'm looking for some inspiration or guidance on a situation with issuing materials to project sites for a client where almost all materials are purchased non-stock, and very little purchased to stock. 

Non-stock purchase requisitions are created at site, and purchase orders generated by a centralised purchasing group. 

Materials left over at end of a project are typically returned to a central warehouse, there they are adjusted into stock at cost.  When purchase requisition is reviewed by the buyer, decision may be made to supply some or all of the requested quantity form the warehouse, with balance being ordered on a supplier.