If the total cost of an improvement project or services is determined, the board shall levy the assessments against each parcel of land against which an assessment may be levied in the district. With regard to an assessment for services, the board may levy an annual assessment that may be lower but not higher than the initial assessment. The board shall have an assessment roll prepared showing the assessments against each property and the board's basis for the assessment. The assessment roll shall be filed with the secretary of the board or other officer who performs the function of secretary and be open for public inspection.
Tex. Loc. Gov't. Code § 375.120