As a custom home builder, I sit down with my potential customer with their house plan and find out what they specifically want in their home based upon their budget for the home. Most minor changes to the plans can be made with no problem.
A tract builder typically has a collection of house plans and designs for the customer to choose from. They also have standard and upgrade packages. Because they generally build the same house over and over again, their plans are pre-priced with standard options. The customer can then add upgrades as they desire and can afford. Many times a customer will find a tract builder to not be as flexible in making requested changes. In most cases if the tract builder has actually developed the subdivision they are building in, they don’t have as much money tied up in the lot price (as would the custom builder) and can, therefore, typically build one of their plans at a lower cost. A tract builder tends to not be as flexible as a custom builder.