Oracle Database Discussions

My CIO has tasked me with creating my own set of performance metrics. He basically wants me to create a stop light type of metric where green means the database is running fine, yellow means the database is still running, but it is under some stress and red means the database is very very busy and can't keep up with the work load. I have been keeping the Top Activity window open and monitoring performance there. Does anyone know the tables/views that are used to populate this so I could create a query to poll the information to create my metric?