This report presents an object-oriented programming (OOP) solution for a function room booking system. The report begins with a use case analysis, identifying actors like the Guest, Accountant, and Room Manager, and detailing the main and alternative flows for booking a function room. It then develops a domain model, outlining actors and objects within the system, and illustrates the interactions between them using lifelines and messages. Finally, it presents a class diagram, identifying the main classes such as the reservation class and their relationships, including one-to-many relationships and subclasses like check-in and check-out. The report aims to provide a structured approach to designing an online booking system, addressing the challenges of the manual system and offering a more efficient solution for managing function room bookings.