How can I define bill rates for inventory items

Hello There,

Background: As part of the Time and Materials Project, we have to issue inventory items to a Project and task. A task is created for each field service job. These inventory items are consumed in a field service job. When an item is issued to the job (a project and task), item cost is charged as an expenditure item.

Issue: Our requirement is to bill these inventory items to the customer. In Oracle Projects, you can define bill rates only for labor and Non-Labor (Usage) resources. How and where do I define and maintain bill rates for these inventory items? How does the system determine or calculate the bill amount for these inventory items consumed on a job?