I would like to detect that a building was build.

I need the reference on the building by the event. Then I can use this reference as "triggering unit".

"Any Unit construction is completed" gives me a reference on the worker (SCV).

Event: Unit is created. The reference to the created unit is "Created unit" - it should be in the same category as "Triggering unit".

It's "Any Unit construction is completed" and the correct reference is "triggering progress unit"

Created Unit + triggering unit gives reference to unfinished building in my case.

Hrrm. Try seeing if "Unit is Created" works instead of construction is completed. If not, I'll see if I can find another way.