This is an auto farming structure designed for two villagers. You will want to make sure this is (used to be, do not know now) 70 blocks from any personal bed so that you don't have the villagers breed. There are two villager eggs in the chest if you wish to go that route. It is a good idea to either let the couple fill their inventory so they can replant ( 8 slots of 64 each). Even if the taters are not fully grown you should get a stack when you flush wash it to the hoppers minus any rotten ones. You will figure it out. I hope you enjoy it.
NOTE: If you want other than potatoes then change the crop before the Villagers get their grubby little hands on it. When you paste it faces west.