Building for Grinding Grains
Puzzle 1 of Auction House Hard Pack
Question is: Building for Grinding Grains
and the answer is: GRISTMILL
Word Meaning:
GRISTMILL — A mill that grinds grain; especially, a small-scale local mill that grinds grain brought by a local farmer to be exchanged for the resulting flour (less a percentage).
Definitions from Wiktionary.