Hi @Aran Billen,
You can leverage Power Automate to Create a cloud flow in Power Automate - Power Automate | Microsoft Learn to achieve this. For connectors, you can use OneDrive, Office, and Outlook connectors to iterate through users to determine the usage and send that user an email. However, I would think there is a policy setting in the Microsoft 365 admin tool that will allow you either cap or notify these users as well. I would look into that first.