tablespace free space report
I found the following SQL from community ID 391 in metalink and it states that its right query to find the exact free space available in tablespace considering autoextend option.
sqlplus "/ as sysdba"
set linesize 250
set pagesize 70
col tablespace_name format a20
select a.tablespace_name, SUM(a.bytes)/1024/1024 "CurMb",
SUM(decode(b.maxextend, null, A.BYTES/1024/1024, b.maxextend*8192/1024/1024)) "MaxMb",
(SUM(a.bytes)/1024/1024 - round(c."Free"/1024/1024)) "TotalUsed",
(SUM(decode(b.maxextend, null, A.BYTES/1024/1024, b.maxextend*8192/1024/1024)) - (SUM(a.bytes)/1024/1024 - round(c."Free"/1024/1024))) "TotalFree",
round(100*(SUM(a.bytes)/1024/1024 - round(c."Free"/1024/1024))/(SUM(decode(b.maxextend, null, A.BYTES/1024/1024, b.maxextend*8192/1024/1024)))) "UPercent"