The chairperson of the irrigation board, under the direction of the board, shall make out an assessment roll, entering and describing on the assessment roll all the lots, premises, and parcels of land to be assessed, including on the assessment roll all lands benefited by the construction of the irrigation improvement. The assessments shall be based upon benefits to be derived from the proposed irrigation improvement. The irrigation board shall tentatively establish the percentage of the cost of the irrigation improvement which is to be borne by each of the parcels of land assessed on the special assessment roll. After the tentative apportionments and assessment roll is made, the irrigation board shall set a time and place when and where they will meet and hear any objections to the roll.