Think about where you live and where you have lived, and simple things that drove you nuts but could've been fixed or design better with minimal investment. I'm not talking about expensive things like an extra bathroom, I mean simple things that would've been easy to design or build had it been done correctly from start. My examples below: 

Faucets too close to the wall: Drives me nuts when the space between the wall and the faucet is so narrow that it's impossible to clean either. 

Sinks that are too small and/or faucets so big that you cannot wash your hands without touching the side of the sink. 

Countertop with faucet: If a small slope was sanded down from the backsplash towards the sink, water would drain down easily and never need to be wiped down. 

Light switches near doors: This one is so obvious and self explanatory, and any builder that does this should have their license revoked. Seriously. 

Closet off of front door: This one kills me as a Californian . . . . Every front door needs a closet for jackets and closets. I seriously don't know how families do it without their front door looking like a yard sale. 

Looking forward to what some of you suggest!