I think they misjudged the timescale and the complexity added by slope. Good outcome though so clearly wasn't too badly misjudged.

Youtube channel Wild Wonderful Offgrid [1] built a much bigger absolutely gorgous house...but on flat terrain and over two years.

The other thing I've noticed is that many successful projects have pretty permanent "temporary" accomodation on site that take the pressure off needing to complete it asap.

[1] https://www.youtube.com/c/WildWonderfulOffGrid/videos?view=0...