In all cases where bridges shall have been or may be erected for the county and deviations from or alterations in the plan contracted for have been made by the direction of the county commissioners, where the county commissioners and builders cannot agree upon the compensation to be made therefor, it shall be lawful for such builder to recover any sum to which he may be justly entitled for such deviations and alterations beyond the contract price in an action for work, labor and service done and performed and material found and provided.
16 P.S. § 5705