I wouldn't trust something that I made, I would rather save over a period of time and purchase one. If the door mount/anchor works, and it sounds like it is safe, then I might consider that approach. I've 11 foot ceilings so I don't think a ceiling mount would work for me even if my apartment management office approved it....
I just checked out the basic TRX package deal and it does include a door anchor. That is good to know. Eventually I want to get either a TRX for home, or a Bosu...we shall see, but neither will come soon.