My thoughts:
Having owned our present house for over 20 years, I sometimes dream about starting over from scratch and building a new house. Some of the things I've thought about that would make a house more liveable and less maintenance intensive:
Build everything possible out of materials that are durable, low maintenance, and age and weather well. Ideally, masonry exterior walls, metal or concrete tile roof. Same Idea indoors. Buy the best appliances and fixtures you can afford. Anodized metal or vinyl clad windows. Zero-scape (or however you spell it) landscaping, metal instead of wood fencing, etc.
Build your house from the get-go to be energy efficient. If I were building a wood frame house I'd consider building the exterior walls out of 2 x 6 lumber and putting lots of insulation in them. Expensive? Yes, but so is heating and cooling. The idea of passive solar heating mentioned above is a great one. You can do a lot with properly designed overhangs that shade the windows on the southern facade in summer and let in sunlight in the winter.
Storage, storage, and more storage. The one thing our house doesn't have that I wish it had is a basement. Instead all our junk that we're not really using right now but we don't want to throw away. ends up in the garage. I can't even get my cruiser in there to work on it. Grr!. Somebody mentioned building a really big master bedroom. We have one, and it just ends up as storage space. I'd love to have less floor space and more storage. It's a great exercise to do an analyses of your plans before you build anything. Just take a copy of the floor plan and color code what is "served" space and what is service space. You should have a healthy amount of service space in order to keep your dwelling from being cluttered. Large kitchen pantry, adequate coat closets and bedroom closets, built in shelves and cabinets are something to think about carefully. I'd design the garage if possible with 2-3 feet of storage along the side walls, and more on the back wall.