A written construction contract, under which a contractor agreed to build a new house for a landowner at a fixed price of $$200,000,$ contained the following provision:

Prior to construction or during the course thereof, this contract may be modified by mutual agreement of the parties as to "extras" or other departures from the plans and specifications provided by the landowner and attached hereto. Such modifications, however, may be authorized only in writing, signed by both parties.

During construction, the contractor incorporated into the structure overhanging gargoyles and other "extras," orally requested by the landowner for orally agreed prices in addition to the contract price. The landowner subsequently refused to pay anything for such extras, amounting to $$30,000$ at the agreed prices, solely on the ground that no written, signed authorization for them was ever effected.

If the contractor sues the landowner on account of the "extras", who will prevail?