There are plenty of companies that make standard size replacement sliding screen doors for your patio, but the trouble is they often need to be cut to the specific width and height of your old sliding screen door. Unfortunately there's no such thing as a "standard" door width or height.
This makes the sale of a single sliding patio screen door more work than some companies think its worth. But rest assured, if you want a sliding patio screen door replacement, you will find one here. sliding screen doors
Roll-formed sliding patio screen door frame is the less costly form of screen door frame that many builders use on new homes. Try to avoid roll-formed screen door frames if you are buying a sliding patio screen door. Roll-formed screen doors are inexpensive but they are also flimsy. They won't stand up to someone walking into the screen, they will usually bend. It's next to impossible to fix a badly bent roll-formed screen door.
Roll-formed screen doors are most often made of aluminum. The aluminum used in roll-forming is usually quite thin and bends easily. By forming the aluminum into the shape shown it makes it stronger but the aluminum is still so thin it doesn't hold screws very well, and doesn't hold its grip when the corners are installed which hold the door together.
There are some roll-formed screen doors that are made from steel. This gives a great improvement in strength but it does make the door heavier and usually corrodes. A steel roll-formed door needs ball bearing rollers to support its weight. Usually steel roll-formed doors just come with plastic rollers which won't last long.
In order to get around the problem of having to custom fit each screen door to the patio door height, some roll-formed door companies are using an adjustable plastic "shoe" at the bottom of the screen door. There are long slots in the shoe with screws which you tighten after you have adjusted the shoe to the correct height.
The problem with this system is the "shoe" often catches on part of your patio door when you try to open the screen door. The shoe also has only room for the cheapest of plastic rollers which don't have springs to keep them on the track as the door opens.
Extruded patio screen door frame is the style of frame you do want to buy. These use more aluminum and are more costly but they are much stronger than roll-formed screen door frames. The strength comes from the thicker aluminum, the Aluminum is tempered, and the design of the screen frame itself.
Extruded patio screen door frames also stand up to someone walking through the screen door a lot better. Usually the worst that happens is the whole door just pops out and you have to put it back on again.
Extruded screen doors are usually supplied with much better rollers which have springs to keep the rollers on the track as the door opens. The extra strength and stiffness of the door holds brackets and corners much better. The thicker aluminum profile allows room for locks to be installed.