Generate user DDL

The oracle DBA can use these 2 scripts to generate DDL statements for a user with their roles, system and object privileges.

On the other side, with datapump (impdp) you can use the parameter sqlfile=My_file.sql you can easily get DDL from dumpfile:
http://www.oracle-scripts.net/standard-datapump-use/

For Oracle >=10:

clear screen
accept uname prompt 'Enter User Name : '
accept outfile prompt  ' Output filename : '

spool &&outfile..gen

SET LONG 20000 LONGCHUNKSIZE 20000 PAGESIZE 0 LINESIZE 1000 FEEDBACK OFF VERIFY OFF TRIMSPOOL ON

BEGIN
   DBMS_METADATA.set_transform_param (DBMS_METADATA.session_transform, 'SQLTERMINATOR', true);
   DBMS_METADATA.set_transform_param (DBMS_METADATA.session_transform, 'PRETTY', true);
END;
/

SELECT dbms_metadata.get_ddl('USER','&&uname') FROM dual;
SELECT DBMS_METADATA.GET_GRANTED_DDL('SYSTEM_GRANT','&&uname') from dual;
SELECT DBMS_METADATA.GET_GRANTED_DDL('ROLE_GRANT','&&uname') from dual;
SELECT DBMS_METADATA.GET_GRANTED_DDL('OBJECT_GRANT','&&uname') from dual;

spool off

More information for this package in the official Oracle 12c documentation :
http://docs.oracle.com/cd/E16655_01/appdev.121/e17602/d_metada.htm#ARPLS026

For Oracle <10 (runs well too with 10g, 11g):

clear screen

accept uname prompt 'Enter User Name : '
accept outfile prompt  ' Output filename : '

col username noprint
col lne newline

SET LONG 20000 LONGCHUNKSIZE 20000 PAGESIZE 0 LINESIZE 1000 FEEDBACK OFF VERIFY OFF TRIMSPOOL ON

spool &&outfile..gen

prompt  -- generate user ddl
SELECT username, 'CREATE USER '||username||' '||
       DECODE(password, 'EXTERNAL', 'IDENTIFIED EXTERNALLY',
              'IDENTIFIED BY VALUES '''||password||''' ') lne,
       'DEFAULT TABLESPACE '||default_tablespace lne,
       'TEMPORARY TABLESPACE '||temporary_tablespace||';' lne
  FROM DBA_USERS
 WHERE USERNAME LIKE UPPER('%&&uname%')
    OR UPPER('&&uname') IS NULL
 ORDER BY USERNAME;

SELECT username, 'ALTER USER '||username||' QUOTA '||
       DECODE(MAX_BYTES, -1, 'UNLIMITED', TO_CHAR(ROUND(MAX_BYTES/1024))||'K')
       ||' ON '||tablespace_name||';' lne
  FROM DBA_TS_QUOTAS
 WHERE USERNAME LIKE UPPER('%&&uname%')
    OR UPPER('&&uname') IS NULL
 ORDER BY USERNAME;

col grantee noprint

select grantee, granted_role granted_priv,
       'GRANT '||granted_role||' to '||grantee||
       DECODE(ADMIN_OPTION, 'Y', ' WITH ADMIN OPTION;', ';')
  from dba_role_privs
 where grantee like upper('%&&uname%')
         UNION
select grantee, privilege granted_priv,
       'GRANT '||privilege||' to '||grantee||
       DECODE(ADMIN_OPTION, 'Y', ' WITH ADMIN OPTION;', ';')
  from dba_sys_privs
 where grantee like upper('%&&uname%')
 order by 1, 2;

spool off