The special inward sloping design, plus a super strong base, could have helped it survive all kinds of natural disasters like earthquakes, heavy rains, and constant pressure from its own massive weight.
The most famous member of this species, Lucy, shows a ton of two-legged adaptations: A human-like foot, a short pelvis, and a femur that angles inward for a smoother stride.
It's a small house, it's a gabled house, so you have the walls go up maybe four feet and then angle in and then there's a flat ceiling at the very top of the room.