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All the answers to these questions can be found in the search function, but me being the good guy that I am, I will help you.
As a newbie, you will use more solution than somebody with experience. Most will use between 30-40 gals of solution per roof. You will probably use 50-60 gals. The solution may be good the next day, depending on what surfactant you use and/or if you add alcohol. See "apple sauce" in the search function for the mixture.
Hope this helps!!  You're welcome!
Gary