Michael,
I bought an use a petzl BOD harness, while it isn't just the lightweight kind I have for rock climbing my reason for buying was to have a serious harness that had multiple attachment points depending on need and really has my safety in mind.
While I like my mammut harness for rock climbing and I have used it a bit when I first started this line of work, I prefer the petzl as no matter which way I might fall it is going to hold me. Obviously rock climbers fall daily as part of the natural way of the sport, but on the job I want to know I'm rock solid. I have several ropes and bought additional static lines for roof work where I don't want the spring and stretch of the climbing ropes.
Also bought petzl descenders last year and have a ton of ways to rig anchors now, personally while I'm still cautious every time, this has made roof work (especially the metal type) far more enjoyable.
I have a healthy fear of heights and a very serious respect for the value of life, so I don't mess around, love the petzl bod, a bit more weight and expense but my life is worth everything to me and my loved ones.
I've looked into courses as well, petzl and others offer access ropes courses for everything from wind turbine towers to closed space, and a variety in between.
I don't feel I know enough yet to be 100% safe, but I always double anchor and when I have added concern I utilize two ropes and other anchor types on the roof itself.
Might not have gotten to your question, but hope that helps.
Justin