Start with icing. Melt margarine in the top of a double broiler; add cocoa and stir until dissolved. Sift confectioners' sugar and add gradually milk; stir until smooth and allow to stand over, hot in boiling water while preparing the pudding mix. Remove from heat and add vanilla. (can substitute a container of chocolate frosting)
Mix pudding and cold milk; stir in cool whip. Line the bottom of a 9x12-inch dish with whole graham crackers (you may "custom fit" the edges with cut pieces of whole graham crackers). Add a layer of pudding, and then a layer of graham crackers, a second layer of pudding, and top with a third layer of graham crackers. Ice cake and refrigerate.
