After the classification of lands and the ratio of assessments of the different classes to be made thereon has been confirmed by the court, the board of drainage commissioners shall ascertain the total cost of the improvement, including damages awarded to be paid to owners of land, all costs and incidental expenses, and also including an amount sufficient to pay the necessary expenses of maintaining the improvement for a period of three years after the completion of the work of construction, not exceeding ten per centum (10%) of the estimated actual cost of constructing the drainage works or the contract price thereof if such contract has not been awarded, and after deducting therefrom any special assessments made against any railroad or highway, and, thereupon, the board of drainage commissioners, under the hand of the chairman and secretary of the board, shall certify to the clerk of the superior court the total cost, ascertained as aforesaid; and the certificate shall be forthwith recorded in the drainage record and open to inspection of any landowner in the district. (1909, c. 442, s. 31; 1911, c. 67, s. 8; C.S., s. 5351; 1923, c. 217, s. 4.)