Ah, I see now that it it C-Channel studs.
I'm on an iPhone and it wasn't clear until I saved the photo and enlarged it.
There's several threads regarding metal studs on the forum, and I think they're a great idea!
I once saw an outdoor patio kitchen constructed of metal studs, skinned with cement board, then finished out with brick veneer.... You had to really dig around to see that it wasn't a solid brick built kitchen!
Anyway, there's a YouTube video of a guy kinda sorta explaining the cuts needed to follow the roof radius...