One Night at a Restaurant,Mark and Mary Wrote Up an Agreement

One night at a restaurant,Mark and Mary wrote up an agreement on a couple of napkins about a construction project whereby Mark would build a room addition to Mary's house.Mark said he would do this in exchange for Mary agreeing to marry him.It took two napkins because the agreement would not fit on a single napkin.On one of the napkins,it was stated that the addition would be built according to plans "that are drawn up on a yellow pad at Mary's house." Mark signed one of the napkins,but Mary signed neither.The contract price was $30,000.A few days later Mark saw the plans,which were more complex than he expected.He told Mary that he could not do the addition.Discuss Mark's claims that Mary did not sign the agreement,there is no sufficient writing,and that the parol evidence rule keeps the plans out of the agreement.