Some custom home builders will only build on client's land, while other custom builders have their own land or lots that they will include in the cost of the project. If you are a home buyer that currently doesn't have a parcel of land or a lot you may be able to get a great price on a lot owned by the builder.
Some custom home builders start with a stock plan and then add on addition, modifications and customize the design. Other custom home builders will work from scratch using the services of a architect or other design professional. It is somewhat less expensive to go with modifications rather than a completely new plan, but also has more restrictions as to final design.