The exterior does look like shou sugi ban wood which (done properly) should indeed last for a long time.

However long it lasts, it would last longer protected by an overhanging roof.

Reasonable conclusion. Without an overhang and gutters it seems like more rain and snow would run off the side of the building than there would be otherwise, keeping the wood wet for longer. But, on the other hand, the green roof might have some characteristics or affordances that prevent that. Hard to tell. I am curious now though!