Ford Motor Company's Rouge Center in Dearborn Michigan has a "living roof" on the Dearborn Truck Plant final assembly building. It is the largest living roof in the world, encompassing 10.4-acres. The living roof is made from living grass and its primary purpose is to collect and filter rainfall as part of a natural stormwater management system. It also provides cooler surroundings and offers a longer roof life than a traditional roof. The cost of the company's living roof and its sustainability efforts would fall into which function in the value chain