How to monitor TEMP tablespace resource usage?

-> Check Total TEMP usage:
SQL>
SELECT B.TOTAL_MB,
       B.TOTAL_MB - ROUND (A.USED_BLOCKS * 8 / 1024) CURRENT_FREE_MB,
       ROUND (USED_BLOCKS * 8 / 1024) CURRENT_USED_MB,
       ROUND (MAX_USED_BLOCKS * 8 / 1024) MAX_USED_MB
  FROM V$SORT_SEGMENT A,
       (SELECT ROUND (SUM (BYTES) / 1024 / 1024) TOTAL_MB FROM DBA_TEMP_FILES) B;

-> Check Total TEMP usage according to database blocks:
SQL>
SELECT DISTINCT S.SID,
                  S.USERNAME,
                  U.TABLESPACE,
                  S.SQL_HASH_VALUE || '/' || U.SQLHASH HASH_VALUE,
                  U.SEGTYPE,
                  U.CONTENTS,
                  U.BLOCKS
    FROM V$SESSION S, V$TEMPSEG_USAGE U
   WHERE S.SADDR = U.SESSION_ADDR
ORDER BY U.BLOCKS DESC;

-> Find problematic SQL for TEMP
SQL>
SELECT 
      S.SID
     ,S.CLIENT_INFO
     ,S.MACHINE
     ,S.PROGRAM
     ,S.TYPE
     ,S.LOGON_TIME
     ,S.OSUSER
     ,SQ.SORTS
     ,SQ.DISK_READS
     ,SQ.BUFFER_GETS
     ,SQ.ROWS_PROCESSED
     ,SQ.SQLTYPE
     ,SQ.SQL_TEXT
 FROM GV$SESSION S    
    , GV$SQL SQ
WHERE S.SQL_HASH_VALUE = SQ.HASH_VALUE
  --AND s.inst_id= 1
  AND S.SID = 555 
  AND SQ.INST_ID= S.INST_ID;

How to define and drop temporary tablespace?

Please execute the commands as "sys";

SQL> CREATE TEMPORARY TABLESPACE ALPER_TS_TEMP TEMPFILE 
 'C:\tablespaces\data_01.dbf' 
 SIZE 8000M 
 AUTOEXTEND OFF
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M;

To alter the tablespace:
SQL> ALTER TABLESPACE ALPER_TS_TEMP ADD TEMPFILE 'C:\tablespaces\data_temp_new_02.dbf' size 128m;

To drop the tablespace:
SQL> DROP TABLESPACE ALPER_TS_TEMP INCLUDING CONTENTS AND DATAFILES;

Used Oracle Version and OS: Oracle XE and Win7

Ref: http://onlineappsdba.com/index.php/2008/02/08/tablespace-and-datafiles-in-oracle-database-back-to-basics/