Need to replace a rotting exterior door frame. The door is on a three season room door that is attached to the house. How do I reconstruct or replace this door frame? What steps do I need to take to ensure that there will not be moisture or rotting problems anymore. Please help.

Are you asking what material to use or information about how to replace the frame?

I would use either the better grade, treated deck boards trimed to the proper width, or there is available at most home centers a solid extruded vinyal material that is not suppose to crack, rot or peal.