Most buyers looking to spend over $400K (or certainly those looking over $500K) will also be considering building a new home.

Typically, the tension between buying vs building is one of:
     1.  Goals
     2.  Money
     3.  Timing

If you build, you can get the house you want, but you'll pay more for it and it will take a lot of time and attention. 
     1.  Goals = Win
     2.  Money = Lose
     3.  Timing = Lose

If you buy an existing home, you won't get exactly what you want, but you will pay less for the house and the process will not be a drain on your time.
     1.  Goals = Lose
     2.  Money = Win
     3.  Timing = Win

Don't let my oversimplification of this issue fool you -- this is something that buyers can get stuck debating for months, or even years, often while looking at resale homes to try to convince themselves to buy instead building.

If you are stuck in this quagmire, I'd be happy to meet with you to talk through some of the pros and cons and try to help you come to a decision you'll be pleased with in the short and long term.