Another thing to consider is that the bathrooms are expensive to change because it means rerunning plumbing lines and electrical outlets, so to avoid costly mistakes when designing a bathroom, answer the following questions before you start design or construction:

1. Will more than one person need to use the bathroom at the same time? If you have two children that will be getting ready for school in the same bathroom at the same time, you may want to consider having a double sink. You may even want to put in a separate shower and tub area from sink area so there is privacy for the shower, but the bathroom can still be used for getting ready. You need to decide what needs you have, and design around those.
2. Do you need lots of countertop space? If you need lots of space for blow dryers, combs, make-up etc, then be sure to include the space for them in your planning, not afterwards. Also, if you need space for all of those things on the counter, you probably need storage space as well. So, determine how much "stuff" you will be storing in the bathroom, and how much space that will warrant.
3. How many bathrooms do you need in your house? You should have at least two, three is most desirable, beyond that is added cost with not much return, but for your family it may be a necessity. You decide what is needed. Along with how many bathrooms, you will want to consider placement. If you have four bathrooms, but they are all connected to rooms, where are your guests going to go when nature calls?
4. Do you want a shower, tub, or shower-tub combo? Decide what is you prefer, and what is ideal. You will probably want at least one tub as many people like tubs and it will help your resale, but if you prefer just a shower, then put in just a shower, it is your house. Family's with small children usually require tubs, as babies, etc don't shower, so, unless you want to live in the house forever, even if you hate tubs, have at least one bathroom with a tub.
5. How much lighting will you need? It is important to have plenty of light in your bathroom, there is a minimum requirement but make sure it is placed in a spot that produces the most optimum light. This becomes especially important to the women who apply make-up in the bathroom. If you are trying to put your foundation on evenly, and you can't see to do it, you might be embarrassed when you leave the house. Avoid this by putting in sufficient lighting.
6. Will you be using water-saving fixtures? If water is scarce in your part of the country, or if you just want to be conservative or reduce your water bill, make sure you install water-saving fixtures from the get go rather than down the road. If you wait to install them you will spend a lot more in labor, and you will be buying parts twice. So, think ahead about what you will want and need, even if that means spending a little extra right now.
7. If you answer these questions before you design your bathroom you will design bathrooms you like better, and that work better for your needs and for resale value. Make your bathroom as efficient as possible with energy, water, etc. and you will not only have a great bathroom, but you will save in utilities as well.