William McDonough is a grand old man in the young field of green architecture.   In the 1970s, he built the first "green roof" in America – a corporate headquarters with a meadow on top – and is now working on a sustainable building for NASA.   Kurt Andersen asks him about the opportunities and challenges of environmental design. (Originally aired: April 18, 2008)                                        Slideshow:   William McDonough's Green Designs

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