The best ways I know to evaluate a builder are:
1. Ask an experienced Realtor what their opinion of this builder's quality is. (Use an independent Realtor, not someone afiliated with this builder, obviously)
2. Ask people in the area who may have experience with a particular builder. Is he easy to work with, does he deliver on time, does he work on the crew or subcontract it all out.
3. Go look at a few examples of his work. Often times you can go to a model home. Look in the basement (if there is one) at the way the home is built, the quality of construction and materials used. Bring someone with you who has some knowledge of how homes are built
4. Look at the finish work, do the moldings match up, are the doors & windows hung straight & true, walls plumb, are there extras included, are the appliances top of the line or middle grade, are there services available nearby, (health care, parks, shopping), is the school district good, how are the houses holding up over time, what about the resale values. There are all things to consider.