Your foundation, crawl space or foundation slab are also very important. Houses with full foundations should have foundation walls that are at least 9 feet 8 inches tall. Crawl spaces should be at least 3 feet tall for easy access. If you are building on a slab, make sure the slab is at least 6-inches thick and contains 58 inch thick reinforcing steel bars placed 2 feet on center in both directions. This steel will help to hold the slab together, so that shrinkage cracks do not widen or offset, producing problems with finished flooring materials.
Bathrooms are very important.
The space created for the toilet should be at least 36 inches wide. If you can provide 40 inches, do so. The minimum width of the bathroom seems to work best if you make it 6 feet wide. Make the bathroom as spacious as possible and try to include a large pantry within the room, not in an adjacent hallway. Try to design the laundry room as a separate room if at all possible.