Overhead cost rules for production

Hello,

I need to add an overhead cost on raw material used in a work order.

We use the AVC valuation method with a calculated cost.

Simple example: I need to add an overhead of 0.05$ per gram, based on the total Raw Mat 1 quantity ALLOCATED in my work order. 

I've played with the Overhead code parameters but can get it to calculted it soully on the Raw Mat 1 item. The system applies the overhead on material, machine and labor.

Can anybody coach me on this one please?

Thanks a million!