At some point you will need to do some work yourself. If you need to set max size, then YOU need to find out how much the database is growing, by day, week, or month. Then determine the max number to set and monitor the growth.

Several options have been suggested. They may not work "as is" but look at them and determine for your situation what will work best. You will learn valuable information about your server and database and gain a better understanding for the future.