Sliding screen doors also come in two frame types. Rollformed aluminum and Extruded aluminum.
Rollformed screen door replacements are the cheaper type. Most builders use these to keep costs down. Unfortunately once they start to get worn they get loose, come out of square and get bent in half. Usually in that order. You want a door that will last longer and be more durable.
An extruded aluminum screen door replacement is a much better choice if you want something thats going to last. Extruded aluminum screen doors are made of thicker material than rollformed doors and have frames with strengthening ribs to prevent them from bending easily when Fido crashes into it.
As well, look for a door that has ball bearing rollers. Most screen doors use nylon rollers but these tend to get brittle with age and exposure to weather. It's a real pain when you spend good money fixing your screen only to have the rollers break apart when you are getting the door back in. Steel rollers will put up with more abuse. They also roll a lot better. Extruded aluminum doors are not indestructible but theydo last for years with normal use and care.
My own "knocked down" screen doors come in a kit form that you can put together yourself. Take a look at the YouTube video below that shows you all the parts that come in the kit. To get a price for one, just fill in the quotation form at the bottom of this page. If you want to rebuild your existing the following instructions apply to just about all screen doors. | 
