If I understand your question correctly, createuser will do this. 'man createuser' ... -D Does not allow the user to create databases.
- [ADMIN] pgsql-admin: disallowing CREATE TABLE Keith Dreibelbis
- Re: [ADMIN] pgsql-admin: disallowing CREATE TABLE Thomas Dean
- Re: [ADMIN] pgsql-admin: disallowing CREATE TABL... Oliver Elphick