Miner

The miner digs down at random and if he gets stuck uses dirt to get out of holes.

Do not place him near sand, or he will die. A lot. When he does die, he'll probably respawn but sometimes seems to disappear.

He will also dig up bedrock, which is something you cannot do in Minecraft except when you are in creative mode. He is likely to fall into the Void when he does, though.

The building's final dimensions (Level 3) are listed below along with the position of the Miner Chest:

X * Z * Y = 11 * 11 * 6