Performa Invoice Based Billing

Dear Experts,

The scenario is related to sales from factory with per-forma invoice only.

Process will be like sales order ----> Delivery -----> PGI-----> Performa Invoice (F8) then later on Invoice (F2) once payment received from customer.

Please share the process for mapping the same so that i am able to generate both performa as well as commercial invoice also.

WR.

Ajay