Hi Richard,
Currently Roon doesn’t support SonosNet and Sonos doesn’t support RAAT. So there is no “out of the box” compatibility between Roon and Sonos.
As set out in this post AirSonos is a freeware program that enables AirPlay to Sonos devices. Roon can then play to those Sonos devices using AirPlay. This article has some further detail. I haven’t tried this myself but others appear to have implemented it and used it.
I know the devs would love to be able to bring Roon and Sonos closer together but no public announcements have been made in this regard. Let’s drop a flag for @mike to see if he can tell us anything.
I would suggest holding off from equipment purchases until you have checked out what can be done with inexpensive Roon endpoints (see this thread.)