The county engineer shall be the custodian of all road machinery and equipment, tools, supplies, and repair parts owned by the county, and he or she shall be accountable to the commission for the same at all times. The commission shall establish necessary policy and regulations governing accountability and relief therefrom. The commission shall furnish the necessary storage and repair facilities for the tools, machinery, supplies, and equipment, and the county engineer shall keep on file in his or her office, at all times, an up-to-date inventory containing a list of all tools, machinery, equipment, and supplies belonging to the county.