The ground here is rarely flat, and a house on a slope is a miserable thing to build. A foundation is a terrace you place like any other piece: its top sits level, a lip above the highest ground it covers, and its skirt follows the ground down and buries itself.
Build on top of it and everything stands square. The top and the skirt take their own facings, so flagstones over a bank of rough stone is one piece, not two.
There is no terraforming in this world and there will not be: the ground is generated rather than stored, so a hole dug in it would have nowhere to live. Foundations are the answer to a slope.