BuddyPress.org

Theming BuddyPress is like theming any other WordPress theme.
You’ll just need to add all the BuddyPress-related template files to your theme for it to be BuddyPress-compatible.

There’s a plugin out there that automates this, BP Template Pack: https://wordpress.org/extend/plugins/bp-template-pack/
However, use it as a guide as it needs to be updated.

There’s also another guide by @thekmen, which can be found here:
http://bp-theme-converts.com/convert-buddypress-theme-to-wp-theme/