Finding Schema size

Query to find schema size in GB
SQL>select
   owner,
   sum(bytes)/1024/1024/1024 schema_size_gig
from
   dba_segments
group by

   owner;
---------------------------------------------------------------------------
OWNER                          SCHEMA_SIZE_GIG
------------------------------ ---------------
APPLSYS                             111.531372
AK                                   .35546875
BSC                                 .297851563
CRP                                 .071289063
IGS                                 4.46289063
OKS                                 .247070313
XNP                                  .19921875
POA                                 .556640625
finding the table size in GB group by owner 
COLUMN TABLE_NAME FORMAT A32
COLUMN OBJECT_NAME FORMAT A32
COLUMN OWNER FORMAT A10

SELECT
   owner,
   table_name,
   TRUNC(sum(bytes)/1024/1024/1024) Geg,
   ROUND( ratio_to_report( sum(bytes) ) over () * 100) Percent
FROM
(SELECT segment_name table_name, owner, bytes
 FROM dba_segments
 WHERE segment_type IN ('TABLE', 'TABLE PARTITION', 'TABLE SUBPARTITION')
 UNION ALL
 SELECT i.table_name, i.owner, s.bytes
 FROM dba_indexes i, dba_segments s
 WHERE s.segment_name = i.index_name
 AND   s.owner = i.owner
 AND   s.segment_type IN ('INDEX', 'INDEX PARTITION', 'INDEX SUBPARTITION')
 UNION ALL
 SELECT l.table_name, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.segment_name
 AND   s.owner = l.owner
 AND   s.segment_type IN ('LOBSEGMENT', 'LOB PARTITION')
 UNION ALL
 SELECT l.table_name, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.index_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBINDEX')
WHERE owner in UPPER('&owner')
GROUP BY table_name, owner
HAVING SUM(bytes)/1024/1024/1024 > 1
ORDER BY SUM(bytes) desc;