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.
Another item which is often missing or lacking in a set of house plans is comprehensive and accurate dimensions. We have always strived to provide more than the minimum amount of house dimensions so that it is easy for the owner and builder to layout a home on its building site. We will even calculate point to point dimensions (using trigonometry) for homes which have lots of odd angles to them (as opposed to a simple rectangle layout). Not all architects or designers will go this "extra mile," so it pays to check these things out beforehand.
Drawing a good set of custom home plans involves integrating many different concepts and ideas into a solid and usable working plan. Many designers are able to come up with a unique or interesting preliminary design, but fail to deliver when its time to detail the house structure. They draw a pretty picture but have little or no understanding of how to translate that nice design into a working plan which the builder can understand.
Moreover, you can save a lot on construction cost when a using a stock house plan. The advantage comes when you purchase a plan that had been previously used. This means all costs have been put into consideration, therefore, one can easily know what to expect come time for the actual construction. This gives an accurate budget, a small construction span, and efficiency due to prior arrangements during the recent use of the house plan.