Rainwater drainage to the stream - Implementation

Hello, we would like to discharge the rainwater into a stream at the property boundary. With the garage and terrace roof, it should be about 150 sqm of roof area to be drained. Permission should not be a problem. I wonder how best to implement this. It is about 35 m across the garden.

Underground PVC pipes would probably limit us when planting the garden because of the roots, right?

Therefore, a surface channel would appeal to me more, but what is best to use for that so it looks good?

How much slope is actually achievable? 35m is already quite a lot..

Slight slope down to the stream and the house itself will also be raised by about 1.5 m to reach street level. Therefore, the gradient should not be a problem.

And why no KG pipe? It is always used and does not cause any problems - it is already at least 80cm deep.

I wanted to plant some medium-sized trees and shrubs, rowan, elderberry, and the like, don't you think they root 80 cm deep?

Yes, and? That bothers neither the plants nor the pipes ;)