Patio door construction has been getting better over the last 30 years. You have to decide on a slider or a French door. Some French doors provide a three point locking system, which is most important to keep out hard weather. Not all sliders ar e the same and we would be happy to explain the differences. We are biased to some doors over others.
Making the patio door weather tight is important and similar to making a window weather tight except for one step, installing a pan below the door. There are several reasons a pan is important. The main reason has to do with dealing with water infiltration through the door threshold. A new door will not have that problem. A 20 year old door may have that issue. Keep in mind that the door threshold receives foot traffic over the years, and due to that traffic it is a high probability it will separate from the jam and allow water to infiltrate. Years ago, all of our pans were made out of copper. Today we have many different products available that will provide the longevity required to do the job properly.