It shall be unlawful for any person to move or relocate a building, structure or portion thereof, except portable storage buildings not greater than twelve (12) feet in width, twenty four (24) feet in length, and twelve (12) feet in height, within the corporate limits of the city without first obtaining a permit from the City Secretary. No permit will be required to move a building or structure being moved over any state or federal highway within the city provided it is being moved under a permit issued by the Texas Department of Transportation and when the moving route is confined to a state or federal highway.