All buildings, including any cement, macadamized, concrete or other improved base or pad upon which vehicles shall stop, park or stand for the purpose of receiving gasoline or oil at an automotive service station, must be set back at least twelve feet from the established street line facing the Commercial District. Any such buildings constructed on the corner lot shall be set back twelve feet from the established street line on the designated commercial street and shall be set back a distance of twenty feet from the established street line of the side street.