Why not measure one of the actual doors you plan to use? Simply bring a tape with you to HD.
Standard framing lumber should do fine for the rough opening. Why not buy a pre-hung unit? There's not much reason to make your own door jamb for a newly built shed.
There are plenty of good books, videos, and plans out there on shed construction. Check your local library.
One thing you might want to look into is to go to the builder supply and see what they have in the junk pile. I got a 3-0 80 steel door for $8 because it had a small ding in it. I mounted it with the ding inside and it looks great. I framed the door with western red cedar. That is a little more bug/rot resistant than garden variety pine and not that much more expensive. It is fairly soft so I used screws long enough to tag the framing members in the hinges
If you are hinging it outward, make sure you get the hinges that have a set screw to keep the hinge pin in, or the type that has pins that intermesh when the door is closed.
Well, when I renovated the chicken coop, I put a couple more doors into it. They are 7' or so tall, and 4' wide. I made some rollers out of garage door idlers welded to brackets, and run them on a grooved 2x4. As I am parking my John Deere in there now, I put the big doors opposite each other. That way, I don't have to back in, or turn around, and can just pull through. Also it makes it REALLY easy to get to the wood I have stored in there. I made the doors out of some 2x2 stock (Ripped from a 2x4) and sheets of 5/8" plywood. They have been working quite well for a year now, and, I expect that they will continue to do so. It is not hard to do at all... As for the jamb. For a storage shed, I would strongly suggest aluminum. It will likely be exposed to a LOT of sun, wind and rain, and kind of by definition is veyr close to the ground. This will expose it to terrible wear, and way too many insects. Aluminum will eliminate rot and maintenance. now...at this point in time, I don't have ANY jamb on my doors, but, that is only because I am not trying to make the chicken coop "airtight". After all, it is not heated space... Regards Dave Mundt
I checked local HomeDepots and cannot find any outswing pre-hung door (open outward instead of inward) and they are very expensive. So I decided to build my own.
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