need a little php script that empties some of my site folders automatically (cron)

hello i have a several folders on my server that receives cached files constantly. it takes a lot of memory on my disk i would like a little script that lets me add the urls of the folders i want to delete content for, and i would like to be able to change the period for this (like every 3 days or 5 days...) this script obviously needs to work with a cron very simple for a very good coder! thanks for bidding :)