Another mildly thematic combo. Warehouse cycles your deck, tossing your Coppers into the discard for the Counting House to pick up. It helps get you to your Counting House faster (through all the Coppers) and also softens the blow of drawing your Counting House too early.
Compared to combos like Golem/Counting House, Warehouse/Counting House is more flexible in that you can buy other cards to help out—Golds and Platinums are always helpful (though of course Bank is the best treasure for use with Counting House), and Worker’s Villages are perfect because their +Buy can provide both the Coppers as well as more buying options later on. Talisman is also a great card for stacking up on Coppers and Warehouses.
The drawback is the ever-shrinking handsize due to repeated Warehousing. Realistically, you won’t ordinarily be able to play play more than 4 Warehouses per turn. But it’s a good solution to the two main problems with Counting House: deck cycling, and drawing the card too early.
An example of how it counters Ambassador quite well.
I didn’t buy much Copper because there
are no Colonies we weren’t going to get to Colonies before the game ended on piles; in games with where Colonies are contested, you should obviously invest a little more in Coppers so you can get to $11.