Fabric Structures are made with a waterproof material that does not absorb water. Everything that hits the membrane slides down. There are a couple of things you can do with the water. You can collect it. You can divert. Or you can allow it to cascade off the edge naturally.
You can collect it by design as in an inverted umbrella or gutter. Depending on the region you live in, you can collect a lot of water and use it for landscaping, etc. You might be collecting it in a gutter to send it to a storm drain or avoid water in a specific area. Gutters and inverted openings are fine but they need to be maintained because trash and leaves can also find their way there too.
You can divert it using a number of devices from rubber to extrusions to clamping to creating fabric sleeves to get water to go where you want it to go. Based the on the design and the slope of the membrane, water will find its way to its lowest point. The low point can be designed as an architectural feature or traditional gutter, leaders and scuppers are used to bring the water to the ground.
The lightest and most beautiful solution is to let the water cascade naturally off the sides. The water can fall to a landscaping, a trench drain or rock bed along the perimeter. This way the tensile structure remains light.
Let nature take its course.