Your question is a bit vague…it all depends on what you are trying to achieve and here I got a few question for you regarding your network and how you want to address these multiple ISPs:
Will there be concurrent connections transparently available to users or are you trying to achieve a fail-over link next to your current one?
Is it a live environment or are you trying to plan the architecture for something that will be?
Is there anything already configured yet? Something to work on or you have to do it from scratch?
I would prefer to know the answers to these questions in order to proceed further.
Also, I’m not really clear on what do you mean with that diagram. Do you want to create a diagram for all this or you just want a guide on how to implement this and you actually asked for a diagram to understand better?
How to manage multiple isp in one network with diagram?