Most people tend to use those assumptions to look online for home designs they like, but there are a few problems with that. Not that it's a bad idea to think about what you'd like to have in your future home!
But it's usually a better tactic to think about the needs and wants of your family, and then build a home based on that, rather than trying to fit your family into some builder's idea of the right home.
It can be easy to fall prey to these challenges if you are focusing on the finished plan of a custom home instead of what your family needs:
In addition to that, it's difficult to know how much it will actually cost to build the design you've settled on without talking to a builder. This plays out in a pretty predictable way a lot of the time.
A family believes anyone who tells them they can get it all for their budget, even if common sense or their gut tells them it's not realistic. It's human nature to believe what we want to believe. This family reverts to shopping around based on price, because they're not sure how else to evaluate one builder over another.
Unfortunately, the cheapest house tends to utilize the cheapest materials and the cheapest contractors. They hire the cheapest builder because he told them exactly what they wanted to hear, but they find out halfway through that they got exactly what they paid for (but they actually overpaid for it).
You can avoid this scenario entirely, though. Think about what you're actually looking for in a builder. Chances are, you're looking for a builder who will listen to what you want in a home (number of bedrooms, bathrooms, square feet, etc.) and then ask you questions about what drives every one of your needs.
This builder will also ask how important each one of those elements is relative to all the others and help you prioritize them. He will listen to your real pain, real problems, and real desires, and then apply years of expertise to create a home design that matches your exact needs.
Here's what's weird and wonderful: the home design may or may not be what you originally envisioned, but it will be what you want and need. Why? Because the builder has applied his expertise in designing homes for people, rather than just telling you what you want to hear to get your business. He listened to the PROBLEM instead of telling you an easy solution, and with your help and guidance, created the solution that solved your real problem.
Don't feel like you have to find all the solutions to your family's needs on your own. Bring your frustrations to a builder you trust, and talk with them about which solutions you're comfortable with. When your home is built, it will have the solutions you need, even if the solutions aren't exactly what you envisioned.