If you look at Pagodas, the places where ancestors are honored to put that shape in your home is a lot to deal with. It takes a very special person to live in an octagon shaped house. The Native Americans lived in teepees, and I believe the base of the teepees, was a circular shape. The circle is an ideal shape, unfortunately it's not an easy thing to build. It would cut out the corners, as far as energy flow, but I can't say it would be that much better than our squares and rectangles.
Some people place the house according to directions, if they possibly can.
You don't want to be on the top of the hill because the chi would be too strong. Also to have a southern exposure, so that the crops would grow was also desirable. To have a pond of water in the front would be wonderful. This is the ideal, but you can't always do this, even if I start with someone from the very beginning of the planning stage, it doesn't always work because there are roads to subdivisions, rules that don't allow certain things. But, having your front door facing south is ideal.