Most new houses are only slightly custom. You generally start with a floor plan from the builder, and then choose the color of the walls or other minor details. Sometimes a new house is cheaper than a used one because you can move into a used house much quicker, while a with new house you have to wait for them to finish. Usually a new house is more expensive than a comparable used house, but not by much. Even a fully custom home is generally not much more expensive because your builder will tell you what costs a lot of money (if you ask for 8.5 foot ceilings the builder will talk you into 9 foot because those are much cheaper since precut parts are available), and what is insignificant. Generally walls can go anywhere and are cheap to move around.