A roof top vegetable garden, I mean. What a fantastic, creative way to get kids outside and in nature when they have little or no access to the outdoors. Every school, building, house, block of flats etc should have one.
It would take some retrofitting on existing structures but imagine the savings on heating, cooling, groceries, petrol to fetch the groceries.... and then your garden, if you are lucky enough to have one, could be a wildlife retreat, attracting all the birds, bees and insects that help with the vegetable growing. Ooooh, the possibilities.