The board of township trustees may accept donations of labor or material for a proposed road improvement, and in determining which road shall first be improved it may, when acting by unanimous vote and without a petition, take into consideration the amount of such donations. The board may require the persons donating labor or material to enter into a contract that such labor will be performed and material furnished at the time required by the board. Such contract shall set forth the value of the labor or material, and in case of failure to furnish such labor or material the value fixed in the contract shall be conclusive in any suit brought by the board for damages for the breach of contract.