Mich. Comp. Laws § 141.105

Sec. 5. Whenever the governing body of any public corporation shall determine to purchase, acquire, construct, improve, enlarge, extend and/or repair any public improvement and to issue bonds under this act, it shall first cause an estimate to be made of the cost and the period of usefulness thereof, and the fact that such estimate has been made and the amount and period of time thereof shall appear in the ordinance authorizing and providing for the issuance of the bonds.