This thesis investigates how underutilised urban rooftops can be transformed into productive, multifunctional spaces through the integration of water, energy, and food systems within the Water-Energy-Food (WEF) Nexus framework. By treating rooftops as interconnected ecosystems, the study demonstrates how water harvesting, renewable energy, and urban agriculture can work together to improve resource efficiency, reduce environmental impacts, and contribute to urban resilience. Through case studies, technical guidelines, and best practices, the research provides a practical model for designing multifunctional rooftops tailored to diverse urban contexts. The findings underscore the potential of WEF-integrated rooftops to address sustainability challenges in cities while setting a foundation for future projects and research in urban infrastructure optimisation.