In accumulating raw materials costs, companies debit the cost of raw materials purchased in a perpetual system to:

Since you are using Perpetual system it will be debited to Raw Materials Inventory

b) Raw Materials Inventory.

option b. Raw Materials Inventory should be debited

When placing the order and make the deposit (payment in advance) then you should debit the cost to Raw Materials Purchase

When the items reaching your warehouse your software should automatically move this ammount to "Raw Materials Inventory"

This is from Supply Chain point of view.