We built in 2006. Customized walkout ranch from existing plan on our own lot. Five years later, we had a page long list of things we'd do different and it keeps growing. However, it's such a stressful endeavor that we probably won't do it again. Fortunately we built with that in mind. I can retire in this house.
If I built a again, I'd consider the following:
High efficiency wall and roof structure - SIP, foam, concrete. Just not standard batt and stick.
Central vacuum
Two hvac systems - we're running five zones on a three ton.
Casement windows - we have tip in vinyl. Waste of money and energy hogs.
Driveway in front of home - it comes to the side and we can't see who's in the driveway.
4th bedroom - we never use the formal dining
Tech wiring - I'd rather not use wifi for everything