trigger ddl actions in a table

I need a way for logging every action on the system catalog. I must have a
table which shows when a tables was created or updated or deleted. I need
the date of the change .

I tried to make an trigger on pg_catalog.pg_class but this throws an error :
"ERROR: permission denied: "pg_class" is a system catalog".

I can see all ddl in my log files, but
- there are even the errors in and
- i can't use it for a select

Is there an possibility for having such an system-action table??

Thanks

Monika König