Toyota Roof Gardens has developed the TM9 self-watering turf mat, a system composed of 20 inch squares of grass on an irrigating base.
Green Geek notes: "Green roofs are a concept familiar to most people now, they've become very popular in recent years on many buildings. As with any environmental feature, there are costs associated with the installation and maintenance in order to enjoy the benefits of the green roof. This may change with a new product that makes adding a green roof as easy as laying carpet."
Time to throw in a little extra for the gardener and find the appropriate garden furniture.