I agree with most of the points made above and would add core strength to the list.

If you toprope/follow enough roofs at a similar grade, you'll probably get a good sense of what you are capable of, which will lead to you feeling confident and, importantly, relaxed, when on lead. There are a lot of roofs you can TR even if you are the only leader in your party, especially if you are willing to be lowered down from a top anchor.