Bifold Door Plans
When we built our hanger, I too looked at building our door. They are really not very complicated. But, after pricing all the required materials, I found it wasn't but a few hundred dollars more go ahead and buy one from the people who build them all the time (don't want to plug any particular MFGR!). If you don't locate any plans, take a walk around your friendly nieghdorhood airport with a pad and tape measure. I'm sure you can find someoone who'll let you make some notes and sketches of their door.
Good Luck!