Hi Ajay,
In our last project we have implemented the following flow where the orders were processed only after getting the payment from customer.
We generated pro-forma invoice from Sales order with required copy control in following steps:
Create Sales order with Availability check so that payment can be taken only for confirmed qty
Generate Pro-forma Invoice
Once you receive the payment,
Process for Delivery and finally Invoice.
The other option in standard SAP is Pro-forma invoice with reference to outbound delivery. Here in copy control you can mention the requirement of with or without PGI.
Let us know if you need additional information.
Regards,
Amit