Go buy a bunch of home plan magazines and find a plan that will either work as is or can be modified with very little work. You will be a lot better off in the wallet by going this route. If you contract with an artichoke, it will get expensive.
Once you find a plan that will work, order up a set of prints and make sure it will fit your needs. Try using scale cutouts of your furniture, fixtures, cars, lifts, etc. to see how they fit the space. If everything still looks good, order up some working sets and have at it.
I agree with everything said by GeorgiaHybrid.
Assuming you've owned homes or at least lived in homes before you have a good idea of what sort of spaces you want, how well they will work for you and your things and what your priorities are. Using scale cutouts and measuring things you have that will go into the house will go a long way toward making sure it will be workable for you.
I will add that many if not most of the home plan magazine plans are available by looking around online. You need to find one that not only works for you space-wise but that has a architectural style that you like, fits well on the lot, etc.
Beyond that changes can always be made. Garages can be easily enlarged, roof lines modified and even floor plans adjusted. Of course these changes will entail costs but likely much less than an architect starting from scratch. You will also likely need to have the plan checked by a local structural engineer to insure it meets you local building code.
In addition to doing your homework above, no matter how you get your plan created, finding a good builder is key. The builder often has the resources either in-house or close at hand to help you make the adjustments mentioned above. A good builder can build about any home to be as energy efficient as you want. If you want to go whole hog on energy efficiency or green building you'll need to find a builder who specializes in these areas. An architect can put all this stuff on paper but if you don't have someone who understands putting it into practice you will end up very frustrated. Personally I think that the builder is just as important and maybe more so than the plan.
Good luck with your new home build. I know many people who say it is a nightmare but in my and my wife's experience it can be a very enjoyable process.
