As soon as said board of commissioners shall have formed its plan and shall ascertain the cost of improvement, it shall file the same with the clerk of the board of supervisors. Said plans shall be accompanied by a map showing the location of all the main and lateral ditches, and shall be accompanied by specifications describing the character of the improvements to be made, the width and depth of the ditches, the probable quantity of earth to be removed, all other work to be done, and the probable cost of draining said territory. Whenever federal financial or other assistance is furnished in connection with the planning or construction of the proposed improvements, such plans and specifications shall be detailed only to the extent required by the federal department or agency responsible for furnishing such assistance.