When you repair a damaged porch floor, be sure to support the roof while you work. Remove existing posts and then nail two 2"x6" to a make a 4"x6" beam. Support the beam with a 2"x4" post and nail in place. Measure two 2"x4"'s to the legnth you need and nail them together at the tip. Prop under the other end of the beam and spread the legs on a base footing until the roof is supported. Attach a cross bar and toenail the base.