Hi Amanda, I think you're looking for an A frame plan to hang a swing from: http://howtospecialist.com/outdoor-furniture/how-to-build-an-a-frame-swing/
Do you want the swing to hang down, (from a ceiling or tree) or are to wanting one that sits on a patio or deck?
Here is a nice one, or you can go for an A-frame..... https://www.youtube.com/watch?v=sGG_nyJYNQc
Today my feed from Hometalk has one I love. Search for "DIY Backyard Swing" on Hometalk.