Re: WPMUDEV Theme question for someone?
Have a look at how it’s done here on buddypress.org (at least on the CSS end of things). https://buddypress.org/developers/boonebgorges/ The nav li items are floated to the left.
As for the PHP, you might have to play around with where the userbar and optionsbar are called in header.php of your child theme. Most of the work is done in the CSS though – the markup is pretty flexible.