"Develop a modern architectural design that transforms an existing structure while maintaining its original form. Focus on enhancing the aesthetic appeal through contemporary materials and finishes, such as sleek glass and metal accents. Integrate modern elements like open spaces, large windows, and natural lighting, while preserving the building's historical character. Emphasize sustainability by incorporating energy-efficient systems and green features, such as rooftop gardens or solar panels. Please provide design sketches, elevation views, and a brief rationale for the modifications."