Many people dream of building a home one day. It's easy to imagine the joys of picking everything, from the type of insulation to the paint colors on the walls. Imagine designing your own cabinetry, deciding how big your closets ought to be, opting for that super cool shower head. Most people don't forget about the important stuff a home has to have, like the number of bathrooms. But there are a lot of little things to think about, too. Here's how to avoid some common mistakes to avoid expensive updates later.