This is a very important question. Many homeowners make a huge mistake in their decision making for several reasons. The best “short” answer is to hire a design-build contractor. This way the plans are included in the price and most legitimate contractors will offer you a firm price in writing, up front, if they know what they are doing. The main reason NOT to hire a separate home designer and contractor is that when there are problems with the project or plans, it is you that will have to go back, have meetings, revise plans, back to the city for approval, print all new plans and get the job started again.
Orange County Construction is a full design/build company that can handle all this for you for one price!