Mac Disk Space disappears with Xamarin Studio

I am a newbie to Xamrin but i am trying to get sample code working and as a result have had to use the Android SDK Manager to install and uninstall various packages. So in one day I have gone from 80GB of free space to 20GB. Can anyone tell me why this is the case when I effectively now only have Android 7.0 (API 24) installed.
Can someone tell me where the redundant files are so I can free up space. This will cause my machine to be unusable very soon.