Pre-drawn house plans are those that are drawn by architects or home designers and then offered for sale, unlike those that are drawn for an individual, with input from the customer. While this method may be a great idea, there are definite benefits to purchasing pre-drawn house plans. Architects and home designers that do custom home designing also do a lot of their own designs, and it is these plans that are offered for sale, They are adept at making plans that utilize available space to the best possible advantage, and at laying out a floor plan to optimize curb appeal.
Every set of custom house plans includes several items which need to be blown up and detailed for further clarification. If a set of plans does not provide additional close-up drawings (for things such as beam connections, deck railings, stairway construction, etc.), then it is not a complete set. It is very easy to cut corners during the planning process. But the end result will be higher costs for the home owner - and lots of frustration for the building contractor.
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.
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.