create temporary tablespace ...

The following is the create tablespace for temporary tablespaces.

CREATE TEMPORARY TABLESPACE {tablespace name}
TEMPFILE '{file name}' SIZE 2000M
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M
/

ALTER DATABASE DEFAULT TEMPORARY TABLESPACE {tablespace name}
/

be carefull with these files as they are sparse. This means that you create a 10g file, but it only uses 128k of actual space. Over time (as the temp tablepsace is used), the actual space used of this file will increase. The problem here is that other files may come along and grab this space so when the temp tablespace wants to use it, it just then runs out of space and reports some non obvious error message.