I recommend adding a slope to your roof, but if it is not possible then try an EPDM roof. Here's one link below:
Search for additional information on the web and definitely call or visit the roofing supply shows in your ara and talk to them about your application.
(1) You need to fix any rotten areas under your current roof (likely if there is a hole, unless the "hole" is really a drain), and
(2) Figure out your drainage plan. The water on a flat roof needs to go somewhere unless you want a swimming pool and mosquito farm!
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