Schema Size in GB

SELECT owner,
  Round(Sum(CASE WHEN SEGMENT_TYPE LIKE 'TABLE%' THEN BYTES ELSE 0 END)/ (1024*1024*1024),2) DATASPACE,
  Round(Sum(CASE WHEN SEGMENT_TYPE LIKE 'INDEX%' THEN BYTES ELSE 0 END)/ (1024*1024*1024),2) INDEXSPACE
FROM dba_SEGMENTS GROUP BY owner order by owner