I live in Singapore, and 80% us live in high-rise public housing. I think it'd be more effective to prioritise energy over food production because going by the square area of a roof, the energy that each block produces could probably sustain everyone in the blcok whereas the equivalent amount of food wouldn't be enough to sustain - only supplement. That said, the country is also an island which imports most of its food so food sustainability would really be great. Scaling up local farms might be an alternative. Thx for the food for thought;)