When the proper municipal authorities shall have been ordered by the governing body to proceed under the provisions of either section seven or section eight of this article, they shall do so without delay. The improvement shall be accomplished, as far as possible without interfering with normal municipal services, with the municipality's regular employees and equipment; but contracts may be made with reputable persons for the improvement. Said authorities shall keep an account of all items of cost connected therewith that affect the total cost of the improvement. Upon completion of the improvement, said proper municipal authorities shall deliver the account of costs to the engineer.