Garage - roof drain is leaking

Hello,

water is dripping into my garage (flat roof with tar paper; or bitumen, I guess it's called) The roof drain is leaking (see the makeshift repair by the previous owner).

My question:
Which craftsmen are responsible for this? Plumber? Roofer? Or who?!?

Best regards,
Volkmann

I would contact a roofer. If it is due to the [Schweißbahn], the drain, or the sealing, he is most likely the one who can fix it. ([Laienmeinung])

What is this adventurous construction under the ceiling supposed to represent and who originally built the garage?

Rhineland greetings

Perhaps the previous owner wanted to recreate the fat corner by Beuys.

I don't know who built the garage. Willi is no longer alive.