Before entering into any Contract for executing any such Work as aforesaid the Commissioners shall procure from their Surveyor an Estimate of the probable Expence of constructing the same in a substantial Manner, and of the yearly Expence of maintaining the same in repair, and each Surveyor shall accompany such Estimate with a Report as to the most advantageous Mode of constructing such Work, whether under a Contract for constructing the same merely, or a Contract for constructing the same and maintaining it in repair during a given Term of Years; and the Commissioners shall Submit the Plan and Estimate of every such Work, together with the Report of their Surveyor, to the Inspector, who shall make in Writing such Observations or Suggestions thereupon as may seem to him to be expedient; and if the Commissioners do not regard or do not act in conformity with such Observations or Suggestions, they shall enter upon the Minutes of their Proceedings their Reasons for not so doing.