I have a rooftop garden. Keeps my room cool, and I get all the herbs and veggies I want. But then, my house is brick, mortar, and RCC, so water isn’t a problem. I have not yet seen it have any effect in terms of seepage, tbh. The only thing someone might be worried about is weight, but then, soil is only half again as heavy as water, and you don’t need more than a foot for growing good crops.