I think people talking about "flatness" are referring to the terrain. Apparently those people can't read, but you clicked a thread with the title Medieval House. Idk when "house" started meaning "terrain" but the flat terrain doesn't even matter at all. The only reason its there is to create a basic atmosphere because the build probably wouldn't looked as good on the Slate floor.
Anyways, the house is really cool, although the ceiling of the interior could use some ramps to smooth it out or something. And the basement's crates are relatively plane. The exterior is great though. :D