If there is valid proof that you signed for another design, then you can seek legal recourse. But if it is worded such in your contract, that the builder reserves all rights to change designs without notification to the buyer, then you are obligated to go through with the purchase. However, you can still consult a real estate attorney to back out of the deal claiming that you as a buyer are not satisfied with your purchase. State law allows that you do not have to purchase a property unless you get what you signed for. Again, recheck the wording in your contract. You can seek legal recourse, notify the builder you are going to do so. Maybe the builder will back down and you can have your earnest money back. Hope this helps.