How to Build a Minecraft Villager Trading Hall

Quick answer

A trading hall is a row of 1-villager cells, each with its own job site block.
Villagers must be able to reach their job block to restock twice a day.
Plan which trades you want first, then how many of each villager you need.

Running between villagers in a village gets old fast. A trading hall puts all your best trades in one safe corridor.

Plan your trades first

Villager	Job block	Why you want one
Librarian	Lectern	Mending and other enchanted books
Armorer	Blast furnace	Diamond armour
Toolsmith	Smithing table	Diamond tools
Weaponsmith	Grindstone	Diamond swords and axes
Cleric	Brewing stand	Ender pearls, bottles o' enchanting
Farmer	Composter	Turning crops into emeralds
Fletcher	Fletching table	Turning sticks into emeralds

Several librariansEach librarian sells a different book. Most halls have 5 to 10 librarians to cover every enchantment.

Build each cell 1 block wide so the villager can't wander off.
Put the job site block right next to the villager so it can always reach it.
Leave the front open at chest height (a slab or trapdoor works) so you can trade but not get stuck.
Light the whole hall and close it in, so zombies can't get in.

No job block, no restockVillagers only restock if they can reach their job site block. If trades stay locked, check nothing is blocking it.

Before you trade with a new villager, break and replace its job block to reroll its trades. Once you trade, it's locked forever.

Cheaper tradesWinning a raid gives you Hero of the Village, which drops prices for a while. Plan big trading sessions after a raid.