(a) If the commission finds in favor of levying assessments, it shall direct the assessor and collector of the district to prepare a roll of all the taxable property in the district in the same manner as assessment for ad valorem taxes.
(b) The assessor and collector shall make an assessment in the proportion of cost to be borne by each item of property on the tax rolls, basing the proportion of cost on benefits to be derived from the improvements by the property and the owner of the property.