You need first to find out whether the doorway has standard dimensions (i.e. will fit a storm door bought off the rack.) Homeowners' manuals in your public library will tell you how to fit a standard-sized door. Non-standard sizes require prior experience.
We have a combination - 1/2 screen for the summer. A glass goes in its place for the winter. We have a small porch so it is not exposed to snow or rain.
Our neighbors have a solid glass door that goes over their front door. None of them have a screen for the summer.
If you are handy you could do this yourself.
Hub is not handy so we had ours installed by a merchant that sells them and installs it.
I've done it too, with three doors. I've used the 'Forever' brand doors and had no problem. If there is a problem, they have actual telephone support, and will even replace parts you might muck up during installation. Install the frame top and sides, hang the door, then install the handles and locks, weather seal, and the pistons. There's a bit of fooling around to get it to close the way you like. Last, there's some plastic trim to conceal the screws. For a fat-hand like me, that's the hardest part.
Most are easy to install unless you have unusual circumstances. Lowes carries (among others) Larson storm doors which are excellent quality and come in a variety of styles and pricesw. The most common standard sizes are 36" and 32", but it's not impossible to find 30".
We had one of the Larson Williamsburg model which was a truly beautiful and extremely well made door. We had it for 8 years when we sold the house and it still looked like new.
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