The board of county commissioners may also invite, receive, and consider bids on any other plan at the option of bidders, and shall require that any such plan together with specifications shall be filed in the office of the county auditor for a period of fifteen days prior to the date for receiving bids. Such plans and specifications shall show the number of spans, the length of each, the nature, quality, and size of the materials to be used, the length of the structure when completed, and whether there is any patent on the bid plan, or any part thereof, and if so, on what part thereof.