Placing House Add-On's, by Levi and Candy
Introduction Tailoring Add-Ons: Loom | Spinning Wheel | Small Bed | Large Bed | Pickpocket's Dip | Training Dummy   Smithing Add-Ons: Anvil | Small Forge | Large Forge   Tinkering Add-Ons: Stone Oven | Flour Mill   Magery Add-Ons: Stone Altar (Abattoir) | Red Pentagram

Flour Mill Facing East
Size of object: 1 tile x 2 tiles
Direction object extends from targeted tile: North
Notes and personal observations:

Had to switch houses on this one because Candies upstairs was a bit messy.
Even though the mill faces East I was unable to place in the corner so I had to conclude that it extended north from the target.
Ovens, Mills and Fireplaces (if they ever become craftable) have to be on the top story of any structure.

Flour Mill Facing South
Size of object: 1 tile x 2 tiles
Direction object extends from targeted tile: East
Notes and personal observations:

Had to switch houses on this one because Candies upstairs was a bit messy.
I believe that the flour mill though facing South actually extends East from the target.
Ovens, Mills and Fireplaces (if they ever become craftable) have to be on the top story of any structure.