Fast-growing Method Homes of Seattle is growing again — this time on the East Coast. Method Homes on Tuesday announced it has opened a 15,000-square-foot factory in Pottstown, Pa., where workers will build prefabricated houses and commercial buildings.Method Homes’ revenues grew nearly 785 percent from $520,000 in 2009, to $4.6 million in 2011. This put the company at the top of the Puget Sound Business Journal’s 2012 list of the 100 Fastest-Growing Private Companies in Washington.In Washington, employees work in a 55,000-sqare-foot factory in Ferndale, Whatcom County. The company launched a commercial division this spring; one of its first projects was Taproot Theatre’s annex at 204 N. 85th St., Seattle.