Script to get tablespace free space including MAXSIZE for datafiles

Hi, gurus. I have scripts that query a 9i database for datafile free space and send emails listing available space per tablespace. The trouble is, these scripts do not take into account Used as % of Max. Let me elaborate. For example, the alert shows that NJ_INDEX tablespace is at 100%. It actually is. But once it reaches 100% it will extend by 100MB until it reaches MAXSIZE of 20GB. So, actually there is 18% free because datafiles will expanding until there is no space on device, or maxsize is reached. There is a discrepancy between 100% and 82% if MAXSIZE is considered.
So, the question is - where can I find scripts that actually show "Used as % of Maxsize" per tablespace?