The board of directors, subject to the limitations contained in this act, shall have the power and it shall be their duty to determine what public works, utilities, and improvements are necessary and whether the cost thereof shall be paid from the general fund of said district, or by issuing general obligation bonds or revenue bonds, but before any bonds shall be issued, the board of directors shall cause surveys of work deemed necessary by it to be made, and plans and estimates made by a competent registered engineer, who shall make a report thereof and file the same, together with plans and specifications, in the office of the secretary, which report shall be open at all times to inspection by taxpayers of the district.