Green roofs have become an increasingly popular solution for enhancing urban sustainability and resilience to climate change, offering a multifaceted approach to addressing environmental challenges. These infrastructures help mitigate urban heat island effect, enhance biodiversity by creating habitats for various species, and improve air quality. Green roofs' water retention capability is crucial in reducing stormwater runoff, easing pressure on urban drainage systems, and lowering flood risks, making them an essential tool for sustainable urban design. At the building level, green roofs are recognized for improving thermal performance, reducing energy consumption, and contributing to water management when rainwater harvesting systems are integrated. However, green roofs’ performance is closely linked to local climate conditions, revealing the need to optimize the design solutions, namely regarding hygrothermal behavior. This preliminary study explored the performance of green roofs in distinct southern European climates. The research compared a conventional roof with two green roof designs featuring substrates with different thicknesses using WUFI software. The findings demonstrate that green roofs can significantly contribute to energy efficiency and thermal comfort compared to conventional roofs. Thicker substrates were more effective in insulating buildings and managing internal temperatures. The benefits of green roofs were evident across all climates, but their effectiveness varied depending on regional conditions. This research highlights the importance of adapting green roof design to local environmental conditions to maximize their benefits. By optimizing substrate thickness and considering regional needs, green roofs can be a versatile and efficient strategy for improving building performance and addressing broader environmental goals.