Mining / Cavebuilding in Campaign format

[Enocelot]

Are there any official rules for mining minerals or cave complex building to go with Ultimate Campaign?

[jerrys]

As the last of the battlements is finally consumed by
the mud and water, their stone giant assistant turns to his
sons. "That’s why you should never build a castle in a
swamp."

[Enocelot]

So what's the DC?