Portland's first green roof was built about 13 years ago. Since then, 165 green roofs have sprouted up all over the city, the Oregonian editorial board writes. However, the board notes that Portland could learn from Chicago, Tokyo and other cities that have promoted green roofs aggressively. The board notes that there are still 12,500 acres of conventional roofs in Portland. "This city has only begun to go green," the board writes.