DDL

GENERAL USAGE
-------------
SET LONG 99999999
SELECT DBMS_METADATA.GET_DDL('OBJECT_TYPE','OBJECT_NAME','OWNER') FROM DUAL;

Before droping user:(super Script---> collecting all grants of user)
--------------------------------------------------------------------
set long 100000

select dbms_metadata.get_ddl('USER','&username') from dual;
select dbms_metadata.get_granted_ddl('SYSTEM_GRANT','&username') from dual;
select DBMS_METADATA.GET_GRANTED_DDL('OBJECT_GRANT','&username') FROM dual;
select dbms_metadata.get_granted_ddl( 'ROLE_GRANT','&username') from dual;

SET LONG 99999999
select dbms_metadata.get_ddl('TABLESPACE','&TABLESPACE_NAME') FROM DUAL;

select  dbms_metadata.get_ddl ('TABLE', '<TABLE_NAME>', '<SCHEMA_NAME>') from dual;

select  dbms_metadata.get_ddl ('TABLE', '<SCHEMA_NAME>') from dual;
select dbms_metadata.get_ddl('PACKAGE','<PACKAGE_NAME>','<OWNER_NAME>') from dual ;
select dbms_metadata.get_ddl('PACKAGE_BODY','<PACKAGE_BODY_NAME>','<OWNER_NAME>') from dual ;

select dbms_metadata.get_ddl('PROCEDURE',<PROCEDURE_NAME>','<OWNER_NAME>') from dual;

To get the create scripts of all  tables of  a particular schema
----------------------------------------------------------------
SQL>spool tables.sql
SQL>select 'select dbms_metadata.get_ddl(''TABLE'', '''||TABLE_NAME||''',''<schema>'') from dual;' FROM DBA_TABLES
/

http://tech.padipa.net/generating-create-scripts-through-dbms_metadata-package