Due to how permissions are set up and the file quota limit, you'll need to copy an existing group such as the "Normal" group and then customize it.
Here's how to copy a group:
- Open up your TS3 client and go to the "Server Groups" menu
- Right click the group you wish to copy and select "Copy"
- Enter a name of your choice
- Select "New group" from the drop down box
- Select "Regular group"
- Click "OK"