Someone who actually did it recently:

“In all, to rotate this house [cost] roughly $350,000 extra on top of the land and the house itself.”

The guy who’s 26 year old plans were used:

Mr Everingham estimated his design would cost approximately $150,000 on top of a normal house build.

This is a case of an elderly person drastically underestimating inflation of housing construction…

It costs 350k