The two-alarm fire began around 5:30 a.m., and within a half hour the roof had collapsed, forcing firefighters to battle the blaze from the exterior.
Crews had the fire knocked down within an hour of its start, said Helen Fitzpatrick, spokeswoman for the Seattle Fire Department.
There were no reports of injuries.
Emergency crews closed 4th Avenue South to traffic.
Television stations showed flames engulfing the building, near Safeco Field, as a thick column of dark smoke drifted over the city.
Firefighters stood atop a two-story building adjacent to the warehouse and sprayed water to prevent the fire from spreading.
A sign on the front of the building read, ``Environmental Home Center.''
A search of the Internet showed the 12-year-old company offers environmentally friendly building supplies, including flooring, cabinets, natural-fiber carpets, and low-toxic paints.
