How to validate column while creating Table?
PostgreSQL does not support triggers on system tables, so there's no way you can write a normal trigger that fires when table definitions are changed.

PostgreSQL 9.4 introduces a new feature called event triggers. (More options have been added for event triggers in the coming 9.5 release too). You could use an event trigger to validate that table definitions follow rules you set out by writing suitable validation code in PL/PgSQL. You can query information_schema and/or pg_catalog to find details of the tables, and you can abort the transaction with an ERROR if you don't like what you see.

That said, this seems like a complicated technical solution to a simple people problem. I wouldn't advise going down this route when your code review process can be fixed to catch these sorts of problems, your app can be modified to query the schema and emit warnings on tables that aren't defined how you require, etc.