Calculation of buffer volume for retention of stormwater

Hello everyone,

I have to temporarily store rainwater on my property, and the volume depends on the connected, paved area (3m³ per 100m² of connected, paved area). Since the property is not very large, a retention basin is not an option, but a retention cistern is.
Now my question: Does the connected, paved area only include the surfaces of the house and garage roofs, or also the area of the terrace and garage driveway? Or does "connected" here really mean that only areas connected to the cistern via a gutter or similar count? I am not concerned about the rainfall fee, just that I know how large my cistern needs to be.

With a roof area of garage and house of 180m², I would thus need a retention cistern of 5.4m³?

Thank you very much

Access paths, terrace, and the driveway should also count. Basically everything where a drainage channel is connected.

The draft plan states that the garage driveway is drained via the green strip. Or what does it depend on whether the terrace and courtyard driveway are drained via a channel or not? As far as I know, no channels are planned so far and the slope is from the garage to the street.