This alert uses the system view named DBA_TABLESPACE_USAGE_METRICS (Oracle 11.2+) to calculate the free space remaining in all tablespaces. It includes both data and temp tablespaces as well as takes autoextend data files into account.
To create this alert, click on Alerts > Manage Alerts tab and create a Custom Alert of type Custom SQL Alert - Multiple Numeric Return. Configure the alert similar to below.
Alert Name: Tablespace Free Space
Execution Interval: 1 Hour
Notification Text: The following list of tablespaces have less than 5% free space remaining.
SELECT tablespace_name, 100-used_percent
Execute Against: Monitored Instance
Units: % Free
High Threshold: Min 5, Max empty
Medium Threshold: Min 5, Max 10