When a building or structure or any portion thereof is, upon inspection by the Building Commission or its agent or agents, found to be an unsafe building or structure as herein defined, the Building Commission shall issue a complaint setting forth therein the condition or conditions prevailing in such building or structure which render it to be an unsafe building or structure as hereby defined and directing the repair, alteration, improvement or the vacating and closing or removal or demolition, or any combination thereof, of such building or structure, as the case may require, within a reasonable time to be set by the Building Commission. Such complaint shall further set a time and place for hearing at which time all interested parties may appear and be heard.