This advanced STEAM project challenges students to become green architects and energy analysts as they design a calculator that simulates building energy use and renewable energy integration. Using Excel or web-based tools like HTML, students model how factors such as weather conditions, insulation materials, energy-efficient appliances, and recovery systems impact overall energy demand. The calculator also evaluates how much energy should be supplied by renewable sources and how much excess energy could be stored or returned to the grid. Once the model is complete, students apply it to design a high-performance, net-zero energy building. The final step brings their concept to life: building a scaled mock-up that showcases their eco-efficient architecture. Along the way, students strengthen skills in data modeling, sustainability, systems thinking, and hands-on prototyping, while developing solutions to real-world environmental challenges. This project is ideal for aspiring engineers, architects, and future sustainability leaders.