In designing a sustainable residential building for a big city, I would include these key features: 1) Energy-efficient designs, such as passive solar design and natural ventilation, 2) Green roofs and vertical gardens to improve air quality, 3) Rainwater harvesting and greywater recycling systems, 4) Solar panels and other renewable energy sources to minimize the building's carbon footprint, and 5) Use of sustainable construction materials to reduce environmental impact.
You are an experienced architect. Imagine you are designing a sustainable residential building for a big city. What key features would you include?