Well my arch tool seems to be confused on what it should do. What its currently doing is creating sort of a partial cylinder with all of the vertices slightly off of a curve. Will post a pic in a bit once i get a chance.
Make sure it all measure equally e.g 128 x 128 x 128
It’ll look fine, there’s an option for it as well related to this but I forget where as not at home in Hammer…
make it a cube first and make the wall thickness lesser.