Atlanta celebrated the installation of a 3,000-square-foot garden on the roof of its City Hall in December. The $60,000 green roof project was sponsored by the city's Department of Watershed Management as a tool for improving air quality and for reducing stormwater runoff. The garden is accessible from the building's fifth-floor cafeteria and serves as an outdoor patio. Chicago, Portland, Ore., and Seattle also have green roofs on their city halls, and Anne Arundel County, Md., and Arlington County, Va., have installed similar projects on county buildings.