If you have OEM, this repository query may be very helpful:
SELECT KEY_VALUE Tablespace_Name,
ROLLUP_TIMESTAMP Sample_date,
METRIC_COLUMN metric,
AVERAGE
FROM sysman.MGMT$METRIC_DAILY
WHERE metric_name='tbspAllocation'
and TARGET_NAME='<dbname>'
and KEY_VALUE = '<tablespacename>'
ORDER BY 1,2,3;
