The design of your house is a very personal and complicated process. You have several methods of getting it done. You can buy "stock" house plans from a book, have your builder either draw up your ideas or use a design he as built previously or hire an Architect to do the work.
Each method has it's pros and cons. Certainly the house plan books or working with your builder will be less expensive but you may be surprised at what you don't get! Most of those plans are sketchy and usually just what you need to get a permit and get the house built. Unfortunately, a lot of details will not be included and you will find yourself making thousands of decisions to nail down EXACTLY what you are getting. In addition, you will have no way to verify the safety or quality of your home and no jobsite observation.
If you want a custom home, hiring an Architect will assure that you get what you expect. In addition to the planning phase, a good residential Architect will help you select a contractor, observe inspections, handle changes and cost overruns with the contractor and assure you that you are getting what you pay for. In short, hiring an Architect is not just for the "floor plans."
Now, while a set of plans from a book might cost you $500, and a builder might charge you nothing for plans, expect to pay substantially more for a residential Architect, depending on the size and cost of the house and the scope of services they provide.
Having said all that, I need to refer you to a residential Architect. It really is an art and while Rockwood Design, PC knows commercial construction inside/out, our residential experience has been limited to multi-family and a few houses for friends and family. I'd be arrogant if I said there is no difference between commercial and residential work or that I can do anything.
I encourage you to read a book "Your New House" by Alan and Denise Fields or any other other "so you want to build a house" book that outlines what you can expect, including the traps and pitfalls. Don't be spooked by what you read...if you and your spouse agree that you really want to build a house, just for you and your family, go for it, but it won't be easy! This book also contains lots of tips on choosing your Realtor, Architect, Builder, Banker and the team that will make it a good experience.
Good luck. Want to see some beautiful design work from a very talented Architect? www.visbeen.biz