So it's all sitting on a layer of small rock so water would drain well. And I'll be making a slope in the concrete so the water should get right at the end of the pad where I'll be making a franch drain / rock walkway to make sure nothing pools too much. Additionally my roof is overhanging quite a bit so the ~40cm are most of the time dry when it rains anyway unless rains gets sideways twice every 5 years or so.