We are building a custom disk usage monitoring system that tracks and alerts users when their disk usage exceeds a certain threshold. The system uses Python 3.6+ as the programming language, Vonage Messages API for sending SMS notifications, and psutil library to get disk usage statistics from the server or local development machine. We set up an arbitrary threshold of 50% of disk usage that triggers an alert when exceeded. The system also includes a bonus section on setting up a cron job or scheduled task to run daily for regular disk checks.