Right on! I've considered this as well. Could be aquaponics too, with fish say on every other floor (or however it works out for nutrient density). Catch rain from the roof, and gravity feed the water down the system. It's so feasible i can taste it. Could integrate composted/ pasteurized black and greywater for nutrients too. So many possibilities. Come on self-sufficient cities! Stewards of their own food supplies!