Remember that plans are not necessarily "as is." Builders can use a reverse set of plans (sometimes called a mirror image) to better site a house. It's also possible to hire an architect or modification service to personalize a plan. Ask if reproducible prints or electronic CADD files are available for the selected plan. Either will make the alteration process quicker and easier.
The field of drawing custom house plans is a crowded and competitive one. There are many architectural and design firms out there vying for a "piece of the pie." However, if you look closely at examples of their finished product, you will find huge differences among them. The better ones offer quality designs and highly detailed plans.
Having a custom drawn designed house means a professional architect applies his skills limited to the individual homeowner's needs or what they have in mind. Factors considered in such a situation are the size of the site of construction, ideas of the individual homeowner, population around the area, and the nationally and locally existing building code plans. Time is also a considerable factor for completion of a custom designed house.
In addition, good stock plans come with a detailed inventory, which you can use while you're developing out your dream house. This is important for two reasons: you can look at the materials used to build your house and determine whether your budget will stretch to accommodate them, and you can get a very good idea of where to upgrade and downgrade materials.