Difficult question that...I designed my very first workout but it was based on a template after reading a book and each exercise was chosen based on what I had available, so some exercise naturally had to be excluded etc. Admittedly it was only a basic routine for conditioning, so very little could go wrong; but it brought my fitness levels up, added muscle and I got what I wanted from it. Even now, I'm still inclined to fall back on it when I'm not feeling great, purely because I know it works.
I don't think I've ever done a routine that has been written by someone else; but, I do take note of what people write, suggest to others in relation to intensity and exercise selection and then incorporate or alter my routines accordingly. LtL said something a few months back and it struck a chord, prior to me writing my routine up, and I heeded the info, even though it wasn't initially aimed at me but was in fact advice given to another member.
I think you have to accept that you're willing to be wrong on occasion, before you should even contemplate writing your own routines...in this way, you're pliable and will listen and learn and alter a routine instead of doggedly clinging to something that may either not work or even be detrimental.