Prior to advertisement for sealed bids, plans and specifications for the proposed work or materials shall be prepared and filed at the principal office or place of business of the agency. Such advertisement shall be made in three issues, not less than seven days between issues, in one or more legal newspapers in or of general circulation in the municipality or county where the principal office or place of business of the agency is located, and in such additional newspapers or trade or technical periodicals as may be selected by the board in order to give proper notice of the receiving of bids. Such advertisement shall designate the nature of the work proposed to be done or materials proposed to be purchased and that the plans and specifications therefor may be inspected at the office of the agency, giving the location thereof, and shall designate the time within which bids shall be filed and the date, hour, and place such bids shall be opened.