BuddyPress.org

You don’t need anything as a starting point for a child theme. Just make a new folder in the themes directory called whatever you want and create a CSS file inside that folder that includes this line inside a comment block at the top:

Template: bp-default

Done. You now have a parent (bp-default) and child (whatever you decided to call it). Start adding CSS rules to override the parent… start adding templates to override the parent templates… etc.