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Deck turns into swimming pool

We have just bought a new house. The timber deck off the master bedroom is lined with butynol. It appears that over time the house has shifted somewhat and there is no longer any incline on the deck, as the water doesn’t run off into the gutter. The waterproofing is probably still intact, but I wonder if we didn’t accidentally open a seam somewhat while we were brushing off the water, as there may be a new (now dry) leak on the ceiling of our family area - however this may have been there the whole time and we just didn’t notice it before?? There is a fair bit of height below the doorframe and a friend suggested building in incline on top of the existing butynol, then waterproofing again and finally adding decking we can actually walk on. We are open to other solutions as well.