This query will give you a basic report on the bytes used and bytes available in the Tablespaces within a particular schema. I have used this script to monitor tablespaces within Oracle APEX but it can be used elsewhere.

In this example the query looks at all Tablespaces that begin with "flow_".

If you wish to query all Tablespaces then remove the

AND lower(a.tablespace_name) LIKE 'flow_%'

SELECT a.TABLESPACE_NAME,

       a.BYTES "bytes_used",

       b.BYTES "bytes_free",

       b.largest,

       round(((a.BYTES-b.BYTES)/a.BYTES)*100,2) "percent_used" 

  FROM 

   (select TABLESPACE_NAME,sum(BYTES) BYTES 

      from dba_data_files 

     group by TABLESPACE_NAME) a,

   (select TABLESPACE_NAME,sum(BYTES) BYTES,max(BYTES) largest 

      from dba_free_space

     group by TABLESPACE_NAME) b 

 WHERE a.TABLESPACE_NAME=b.TABLESPACE_NAME AND 

       lower(a.tablespace_name) LIKE 'flow_%'