Clay is a material very easy to handle and work with. Shaping it into regular-sized blocks and then firing them to make them waterproof allows for an easily available and fast-producing constructing material that can be used for almost any type of building.
Per building level, at the goods' default market prices: the base cost is what the goods it uses cost, the base revenue what its output sells for, and the base profit the difference. Prices in each market move from there.
