I'm a bit confused about the taxes we pay for warehouses. Until recently I thought that the tax is only 280 gold for each warehouse.
Now I clicked my warehouses again, and I see costs of 350 gold or more. Now I'm not sure how to decide when the tavern mission that offers to rent your warehouses is worth accepting (though they usually ask for more space than I can reasonably provide anyway).
I also remember someone saying that it's not worth building warehouses at all (probably on one of the old forums that are gone now). Apparently someone made some calculations and figured that it's cheaper to just rent additional warehouses.