A custom-built home is one where you are in control of almost everything going into the construction of the home. Most custom-built homes begin with an architect who takes your design for your home and produces blueprints. These blueprints become the instructional drawings for the builder. Some builders offer their own architectural services. Others limit their construction to a few select homes, which already have blueprints created.
You may be able to make significant changes to the plans for a new home in a subdivision under construction. Some builders will build new homes in existing neighborhoods to be sold when they are completed. You may be able to make changes to that construction depending on how much of the building has been completed.