There are a lot, and I mean A LOT of high rise residential buildings in Singapore to house our growing population on this small land. Living in one myself, apart from the void decks which allow neighbours to interact, the surrounding parks and open areas do this as well. However, land is becoming more constrained, and the newer residential buildings lack much public spaces around them to allow the residents they house to assimilate naturally with the rest of its surroundings.
This idea jumped up at me because of its novelty. It's ingenious! It creates extra space from the current infrastructure set in Singapore. It seems almost too perfect. Singapore's tropical humid weather supports plant life quite well, and the community is affluent enough to support such an endeavour. Moreover, the practice of growing plants even in high-rise buildings is not new, as many households have pots of plants growing outside their doorstep along the corridors or in their balcony. I believe this practice can be extended to the rooftops where there is more space, better sunlight and where supporting facilities like a greenhouse and draining systems can be built.
New Yorkers have been reported to grow their own corn, cabbages and even tomatoes on the rooftops of their apartments, and either consume their produce or sell it at local farmers' markers.
For the architects and engineers, green walls in buildings have always been explored as a method of beautifying the facades. However, it has not seen much improvement in it's applications beyond aesthetics. This method of rooftop gardening would assimilate seemlessly into the current infrastructure and architecture of Singaporean life and high-rise flats.
The only drawback I see from this is that proper rooftop access have to be given, but I believe this is easily overcome with community support for the idea:)