How to allow users to create and modify tables only in their ownschemas, but with generic table owner

Hi List

I'd like to setup my database in a way that only a superuser may create schemas, then grants permission to a specific
userto create tables inside this schema. This should work so far with GRANT CREATE ON SCHEMA ... TO user_a. However I
wantthe table owner not to be the user that creates the tables. Instead the owner should rather be a generic role (e.g.
table_owner),and the owner should be the same over all tables of the whole database. This would work, too, if I grant
membershipin role table_owner to all users that may create tables. (The users must issue a SET ROLE table_owner before
creatingtables.) 

What I didn't achieve so far is making sure that user_a who created tables in schema_a cannot crete/modify tables of
schema_bthat were created by user_b. Do you see any way to achieve this, while still sticking to that generic owner
role?

Thanks a lot for your thoughts.

Andy