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.
Why do this, since even stock plans cost you at least a couple of hundred dollars each? Because the right stock plans can save you tons of time and money if you have a talented architect. Most plans are at least partly modular these days, and often you can even order prefabricated sections pegged to a specific house plan.
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.
One item to look for when evaluating a house plans' quality level is the number of structural sections which are shown on the plan. Highly detailed sets of plans will always cut lots of sectional views through the house to show every different roof framing situation. This might mean that 10 or 12 (or even more) sections need to be drawn for a large house plan. And even a small house plan should include 3 or 4 sections minimum. However, many home plans available today (especially plans purchased through inexpensive plan directories) cut corners in this department and only show one or two house section views. This means that the builder will have to guess at the rest of the house framing.