Lead Developer
Hmm, GP isn’t really built with that kind of layout in mind.
However, you could get close to that look by setting a left sidebar and placing your menu in it.
Then you would set everything to One Container (Customize > Layout).
That would get you pretty close to the linked website.
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development