Anything in real estate is negotiable.
With that said, there are some tricks to negotiating with builders. Also, buying a spec home, will typically allow for slightly more negotiation than "custom" building one.
I always recommend that you use a buyer's agent for new home construction. It does not cost you anything, and the subdivision agents ALWAYS work for the builder with his/her best interest at heart.
Please let me know if I can answer further questions, or be of assistance.
Commonwealth Real Estate Associates, LLC