Your customer wants to use requirements grouping in SAP Project System.

Requirements grouping of materials is a process that allows you to plan and procure materials jointly for several WBS elements within a project or across projects. To use requirements grouping of materials, the materials must allow sales order or project stock, which means they must have a special procurement type of E or Q in the material master. An MRP group must also be assigned to the materials, which defines the parameters for material requirements planning, such as lot size and planning strategy. Reference:https://help.sap.com/doc/78f5c353b677b44ce10000000a174cb4/700_SFIN20%20006/en-US/0814c353b677b44ce10000000a174cb4.html