The purpose of a green roof was originally to provide insulation from the cold; this early example is from Hof, Iceland [via wikimedia].
A 1998 example by architect Björn Dahrén for a church in Aligsas, Sweden is similar: a simple sod that insulates a building constructed from trees on the church's own property. Note the bracing required to support the weight of the green roof. [photos by hansn, via flickr]
Modern green roofs typically feature an assortment of plants rather than just sod; this 'rooftop wellness garden' was installed by teenagers with Youth Ministries for Peace and Justice at St. Joan of Arc Church in the South Bronx. [via urbanee]
The first green roof to also be certified as a wildlife habitat by the National Wildlife Federation was installed by the Christian Reformed Church National Headquarters in Grand Rapids, Michigan. To qualify as a habitat required over 20 different plant varieties, perching structures, a variety of soil depths and gravel swaths to appeal to a diversity of bird and insect species. [via advancedgreenroof]
A new addition to Frank Lloyd Wright's First Unitarian Church in Madison, Wisconsin was given a sweeping 7,000 square foot green roof to complement the angular copper roof of the original building. 'LiveRoof' modules, which come complete with full grown, locally cultivated plants, were used for immediate effect and lower initial maintenance. [source]