There is not one single quality which defines a custom home. It is a combination of features and qualities which define a custom home. Such a home would usually be very lavish with all the modern facilities. Nothing should look ordinary in the house. Every part of the home should be unique and luxurious.
The living room of a luxury custom home should be quite spacious. I have seen homes where the living room is not as big as it should be. It is not a good idea. Every custom home should have a decently sized outdoor area. Of course, space and size are usually subjective. But, they should definitely be larger than a production home or an apartment. More importantly, they should look a lot different than a normal apartment. There should be a sense of opulence when you enter the rooms of a custom home.
Nowadays, smart homes have become a big trend. Custom home are perfect candidates to become smart homes. So, if you are hiring a custom builder, you need to communicate clearly to the builder that you want the home to be a smart home.