In my country such unions are actually mandatory and apartment buildings are collectively owned by everyone living in that building. Active union's are amazing, my building just got a garden and a small bike shed is in the planning. The last place I lived got a whole renovation organize by the union.
No idea what that is. The direct translation to what it is is apartment union. Every resident is a member and we all vote what goes down on the general use areas of the apartment building. People who own their apartment have more leverage with their vote but people who rent have a say as well, most people in my country own an apartment though.
The general purpose areas of the apartment building are owned by everyone who owns an apartment in the building. Renters do have a say in the decision making though.
As for who pays: every apartment union I have been a part of we have a small apartment union charge on our utilities, usually like 10 euros at most. The amount has always been voted on. So everyone living there collectively pays.