A doghouse with a green roof? The Philadelphia Water Department's Chris Crockett says he's seen one.

A little balcony with a green roof? Roofmeadows founder and president Charlie Miller says he's sure there is one.

Yep, green roofs certainly seem to be taking off, as evidenced by today's formal unveiling of the city's newest -- as well as likely its smallest and oddest -- green roof, atop a bus stop shelter at 15th and Market. You can read about it here.

The event just happens to coincide with a green roofs boot camp, sponsored by the Pennsylvania Horticultural  Society and Green Roofs for Healthy Cities, a national green roofs trade association.

Later this year, From Nov. 30 to Dec. 3, the organization will being its annual green roofs conference, Cities Alive, to Philadelphia, cohosted by the horticultural society. How come? "Because there's great community support here for the greening of the city," says Steve Peck, president and founder of the association.

Meanwhile, in the who's-the-best category, the association has released its 2010 report of green roofs installed nationwide by its members -- a clear caveat, but still.  The report looks not at total acreage, but at the acreage of green roofs installed last year. Counting it that way, Philadelphia is fourth in the nation -- behind Chicago, the District of Columbia and New York. Philadelphia installed about 150,000 square feet of green roofs last year.

Overall, growth of the green roof industry in North America last year was 28.5 percent, up from 16 percent in 2009. More than 700 projects were undertaken by association members.