DIY is easy if all you need is a small rectangle screen. Doing a large size one, you want the stronger frame. HomeDepot has the standard size screen door pre-made too.
I had some company to made our screens (door and windows) since I need a door in the screen for open/close the windows. I don't like to take out the screen everything to open/close my windows. My patio door is over-size and the HomeDepot one doesn't fit.
Almost all company who works on screen door do free estimation. But I could tell you they have a big price range from store to store. Better ask first.