Ohio Rev. Code § 6131.41
The acceptance of the bids in accordance with section 6131.40 of the Revised Code shall be approved by the board of county commissioners. Upon the acceptance of any bid for the whole or any part of an improvement, the bidder shall within ten days enter into a contract in writing to perform the work or furnish the material bid for as prepared by the county engineer. The board by an order entered on its journal shall record the time within which the work shall be completed and material furnished, but if an improvement requires both labor and material and contracts therefor are given to different persons, the time of furnishing the material and completing the labor shall correspond with the time provided for its use in the progress of the work. An upper contractor shall not be required to complete his contract until an outlet is furnished by the work done by a lower contractor.
R.C. § 6131.41