If you are a prospective home buyer with interest in custom homes, you need to first identify a builder who is a specialist in custom home construction. Any random home builder will not be able to handle a custom home project. Generally, it is a practice among low quality custom home builders wherein they go for modular construction. This is against the best practices of custom home building. So, when you interview a builder for hiring, you first need to ask him whether he does modular construction or not. It is important to rule out that possibility.
The custom home builder should immense experience in this field. He should have been in this business for at least 15 to 20 years. He should have constructed at least 100 custom homes. The builder should be highly flexible to work with. There should not be any communication problems. Of course, the representatives of the construction firm should speak the same language as you. This requirement is implicit. There should not be any differences of opinion between you and the building firm.