So what is design/build? I could probably explain it best by giving you an example.
Let's say you want to build a house and you want to build it to your specific needs. You need 3 bedroom, 3 bathroom, 2 car garage that is big enough to have a wood shop in it, you really like the old craftsman style and you really care about energy efficiency and you have a budget of $500k. You would come to me with these details and I would work with you from the beginning of design all the way through the project making sure everything is just the way you want it. With this method of building you end up getting a much better experience then the "typical" method of design/bid/build. I'll cover that real quick.
So with design/bid/build you would get a design from someone like a draftsman who hasn't ever built a house himself whether its an architect, or from a house plan store on line. The kicker here is they have no building experience, although they are good at drawing plans. Now you have your plans and you go visit a few builders to get prices. The builders all have their own ideas of what should go into a house, so they bid the house they way they think it should be done. The prices you get back vary quite a bit and you wonder why. After all they all have the same plan. We many times the homeowner goes with the builder who can offer the best price. This can quickly turn into a huge regret. The person who promises you the world and is still cheaper is many times missing a few things or even excluding them intentionally so they can hit you with a few big change orders along the way. I have seen this happen so many times I cant even count.
So I'll leave it up to you. Which would you rather have? A home designed for you with your needs. Gain a friend you trust. Be on the planned budget that was set in the beginning. Deal with one person throughout the project and finish out your project happy over the house you wanted.
Find your own plan that is right for you, doing your whole bid process, hoping your telling all the competitors all the same details. Collecting prices, comparing bids, making sure the change orders are accurate and accounted for, making sure the budget is correct, and always overseeing the project yourself because you cant quite trust the person you hired.
If I were you I would go with a design/build type of project there have been many people who have had a great experience doing it this way.