How do you convert a deal to an invoice?

How do you convert a deal to an invoice?

I am trying to auto generate an invoice when a deal is marked as "closed won" and "payment status" (a custom field) is set to "Invoice". I then want to automatically send the invoice to a client to pay with credit card via the PayPal integration (or another option if one exists that allows credit card). I am using the "payment status" field to differntatie between deals closed won that were payed with cash from those that need to be invoiced etc.

What is the best way to handle this?