Currently Broadcom APM doesn't provide a metric of the Disk freespace Percentage.
APM for Window Monitoring
Here is link to a ACC bundle that can be used with the APMIA agent to provide Percent Disk Freespace metric. It is not support by Broadcom and is a use at your own risk package.
Here is the link to download the bundle:
If there is an issue or question you can provide your comments to the author.