As the construction proceeds, do your best to monitor the correspondence between the house that is specified in the contract and what is actually going up. As busy as builders sometimes are, it is very easy for them to overlook the fact that you wanted a skylight in the living room, an extra 220 outlet in the garage, or even an additional bedroom.
You need to evaluate the warranty language itself. Warranties offered by builders in this area vary widely. Some cover the home for a year after closing. Others cover some parts of the home, typically structural elements, for 10 years. Some cover concrete flatwork (e.g., basement floors and driveways) if there is differential movement of a 1/4-inch or more. Some explicitly exclude any coverage of flatwork. I wouldn’t make a buying decision solely on the basis of the warranty, but you need to know what the warranty covers before you sign.
You need to make some attempt to evaluate the builder you will be working with. This is particularly important if you are going to work with a builder in the construction of a custom home, but it is still significant if you are buying a completed tract home. You need to have some sense of how easy the builder is to work with, whether they build good homes, and how they deal with warranty issues after the construction and sale of the home is complete.
There are several issues that require special attention from those who are considering buying a new home from the builder.