Massachusetts officials are considering a green-building tax credit that could make green roofs more affordable. The measure is supported by Boston Mayor Thomas Menino. While Gov. Deval Patrick has not expressed an opinion on the legislation, a spokeswoman in his administration said he generally supports "low-impact development techniques, such as green roofs." Tax credits have helped boost the number of green roofs in other cities, according to a group that represents companies that build green roofs.