The incident was reported at 9:35 a.m. at a home in the 1400 block of Clayton Street, according to the fire official.
Two of the workers suffered life-threatening injuries.
Building inspectors say the owner did not have permits for the roofing job. Cal/OSHA noted several work safety violations.
Neighbors say the workers lived at the house and were employees of the property owner.
Bay City News contributed to this report.