The evidence was sufficient to support the finding that a stripped down mobile home was a structure, within the meaning of Penal Code 451, subdivision (c) (arson). Shortly before the fire, appellant had removed trusses from the roof, aluminum siding, and sliding glass doors. The Legislature could not have intended a defendant to have obtained a lesser punishment by attempting to take apart a building shortly before setting it on fire. There was substantial evidence that it remained as a standing and constructed structure that had four sides enclosed by some material and a partial roof.