The board of directors may prepare plans and estimates of the cost of a proposed improvement and determine the manner in which the cost of the improvement must be provided. For this purpose the board of directors may propose the issuance of bonds, notes or certificates of indebtedness payable by an assessment or otherwise on the property in the improvement district, bearing interest at a rate which does not exceed by more than 5 percent the Index of Revenue Bonds which was most recently published before the bids are received or a negotiated offer is accepted, payable semiannually, and in such amounts and maturing at such time, not exceeding 20 years, as the board of directors may prescribe.
NRS 539.427