In the above case you dont have permision to create a temp tablespace then you should ask your DBA to do so thats the only option.
When you create an index on a table that already has data, Oracle Database must use sort space to create the index. The database uses the sort space in memory allocated for the creator of the index (the amount for each user is determined by the initialization parameter SORT_AREA_SIZE), but the database must also swap sort information to and from temporary segments allocated on behalf of the index creation. If the index is extremely large, it can be beneficial to complete the following steps: Create a new temporary tablespace using the CREATE TABLESPACE command. Use the TEMPORARY TABLESPACE option of the ALTER USER command to make this your new temporary tablespace. Create the index using the CREATE INDEX command. Drop this tablespace using the DROP TABLESPACE command. Then use the ALTER USER command to reset your temporary tablespace to your original temporary tablespace.