A request for equitable adjustment is relevant for changes in the Government's requirements, or for use with a Changes or Differing Site Conditions clause. It is not applicable to your situation. In fact, your proposed FFP contract would not be FFP at all if any type of price escalation is contemplated. There would be nothing "firm" about the price. Instead, consider using a fixed-price contract with economic price adjustment, as there is concern about significant fluctuations in material costs due to inflationary pressures for construction materials. FAR 36.207(c) and 16.203 explain the applicability and implications of this contract type.