When you build a custom home, you need to strike a balance between having things for luxury and utility. After all, what is the point of having a custom home built which may meet your functional needs but does not meet your luxury needs? You might as well have gone for a production house which servers the same purpose at a lower cost. At the same time, there is no point overdoing the luxury part and running out of money.
With a custom home, a ratio of 40:60 works quite wells usually with 40% for luxury and 60% for functionality. Some people even go 50:50 ratio. But, giving more than 50% for luxury is surely overkill. At the same time, giving less than 30% for luxury is not worth it as well. So, in our opinion, a ratio of 40:60 usually works the best. Of course, the specific details may vary for one family to another depending on the design and other requirements.
A good custom home builder would help you achieve this balance between luxury and functionality while designing and building a custom home.