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.
Having been in the business for more than 30 years, we have seen a large number of house plans which looked good at first glance. However, upon closer examination, many of these plans were found to be lacking large amounts of needed information. If a house plan is not easy to navigate or is not thoroughly detailed, then the builder is left to guess at the designer's intentions. This often means that he will "pad" his bid to make sure that he covers any unknown construction costs that may arise.
You may also find out after looking at several sets of stock house plans that one is your dream house. Depending on your house building plans, this could save you thousands of dollars in architect fees. If you do order a set of stock house plans, check with the company first to see if you can exchange them later if you want a different plan. Some blueprint suppliers will give you up to 90% credit toward a different set if you return the original plans.
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.