Alterra did something similar on parking structure in Vancouver where fresh greens are scarce in the winter. They used a hydroponic system and got lots of funding (debt). They declared bankruptcy 25 million in debt. The major concerns were the cost of infastructure compared to profits from growing fresh greens (3-4 weeks seed to harvest). Growing fruit crops like eggplant would have been economically challenging.
Outside of the wow-factors (urban, organic, local), there was the harsh reality of high overhead costs and slim profit margins.
Tread carefully!