It shall be the duty of the county engineer to do all of the following:
(1) Employ, supervise, and direct all assistants as are necessary to maintain and construct the public roads, highways, bridges, and ferries of the county, prescribe their duties, and discharge employees for cause or when not needed.
(2) Perform engineering and surveying service as may be required and prepare and maintain the necessary maps and records.
(3) Maintain the necessary accounting records to reflect the cost of the county highway system.
(4) Build, construct new roads, or change old roads, but only when ordered to do so by proper order of the county commission.
(5) Construct and maintain all county roads on the basis of the county as a unit without regard to any district or beat lines.