Unless they appear in writing, verbal agreements are not part of the contract. As the Purchaser, you're obligated to pay for and take possession of the home you have contracted for upon its completion. The Builder is obligated to construct the home according to your contractual specifications and to complete the transfer of title. The Purchase Price also includes any agreed to changes in the plans and specifications at the time of the contract signing. Adjustments to the Purchase Price are normal added costs associated with the purchase of a new home.
Builders have their own policies on how Adjustments are handled.
Your Mortgage Lender will provide you with a letter of commitment regarding your mortgage arrangements. This details the specifics of your loan, interest rate adjustments, and adjustment dates. There are many different ways to approach your mortgage arrangements. This will depend on your personal financial situation and your ability to find the best terms available at the time. This generally guarantees that your mortgage rate will not go up even if interest rates have generally increased at the time of closing, but will go down if they have decreased.