Inner sea castles or ultimate campaign? Has this stuff made it to the reference document yet or d20pfsrd site?
The system from UCam seems to be rather decent. But from what I know, it's not on the SRD yet, but should be there eventually.
I suggest that if you want to construct buildings, or towns, or run a kingdom, that it's a really big chapter in UCamp and therefore worth your investment to buy the book, or at least the .pdf.