Section 8. The commissioners, in their return, shall determine and specify the manner in which a new highway shall be laid out or an existing one altered, relocated or specifically repaired, and may specify in sufficient detail the work required so that the same may be completed in accordance with the commissioners' directions, and the time within which it shall be completed, and each town shall perform the work so required within its limits unless other provision is made. They may apportion the expense thereof upon the county and towns, respectively, or they may agree with the towns in which the highway is located or with the department of highways, or both, as to the apportionment of such expense to be paid by the towns, county or state, respectively. The selectmen or mayor shall give notice to said commissioners of the time when the work ordered is begun if so required in the return, and the commissioners or their agents may examine the work as often as may be necessary during its progress to ascertain that it is well done according to the direction of the commissioners, and, in case the town does not perform the work to the acceptance of said commissioners, the provisions of sections fourteen and fifteen shall apply. The commissioners shall transmit to the clerk of each town in which the highway lies a description and plan of the location and bounds thereof within the limits of such towns respectively, which description shall be recorded within ten days by the clerk in a book kept for that purpose.