The board may, on completion of any portion of the improvement for which the contract price equals twenty thousand dollars or more, order an assessment for the proportionate part of the contract completed, and the proportionate amount shall be collected as provided in this article. If the resolution of intention for the improvement provides for the issuance of improvement bonds, the bonds shall be issued and delivered to the contractor for the proportionate amount of the contract price so assessed.
A.R.S. § 48-2061