I was up early this morning and was thinking about building an outdoor pull-up/ring station and began a search on google. After about an hour I had compiled this list of instructions and videos to help in my quest. The links below range from good to ridiculous and everywhere in between (Some are just plain dangerous). I have not tried any of the designs and recommend you use your head before using any of them. After reviewing the list, my best suggestion is that if you suck at building stuff or your unsure about those abilities at all, you might want to buy a bar from a company.
If and when I decide to build my own, I’m gonna make sure it’s very sturdy, uses a lot of metal and more than likely uses welds to hold the thing together (I’m not a welder, I’ll have to hire someone). I might even try the stuff made by speed rail, but haven’t decided yet.
Anyway if you’re Mr. Build it, some of these links might help, while others will make you laugh and wonder how long it was until someone ended up in the hospital.
If you don't want to build a pull up bar, check out this great option. This is sold on amazon from CFF and gets great reviews. It sells for $109. I have a similar one, and can say that these work great. I like this model better than the ceiling mount types, because of the limited height between the bar and ceiling. With the wall mount types, you also get enough space away from the wall to do kips, plus the ability to do bar muscle ups if you get there in the future.
Here is a book on pull-ups if you are new to them.