Warning Message before closing the project

Hi,

We have a requirement from the client to get a warning/error message while try to close the status of the project to CLOSED if there are any pending transactions (open PO commitments/Budget variance between cost budget/actual budget, open PO, unpaid invoices, unassigned CIP costs etc.). Can you please explain how to get the warning message to stop the user from closing the project in such cases. Do we need to personalize the form application or use Custom Pll to meet the requirement.

Appreciate your help on the above

Thanks,

Chethan