On a finding by the commission that public convenience and necessity so require it, a railroad shall be required to build a spur track to serve elevators, warehouses, mills, or like structures, at the expense of the party desiring the spur track to be built. The person desiring the construction of said spur track may be required by the railroad to deposit the estimated cost of the spur track with the commission before the railroad can be required to construct said spur     track. The person desiring said spur track may be charged a monthly charge by the railroad for the cost of maintaining the spur track and the switch.