Yes it would work.  You could either keep them powered via the USB C socket or maybe get one of the Sonos Charging bases.  They are magnetic and means you can easily move the speaker about and then return to the base with ease.

The Roam is very resistant, but is not designed to remain outdoors permanently in all weather conditions though.  I  would bring it inside when not in use.

Thanks, so I have a garden building with an overhanging roof so was thinking about fixing on the underside of the overhang if that makes sense.

Do you think that would be ok?

Would bring it in for long periods of it not being required, like over winter for example?

As @melvimbe said the Roam is not designed for permanent outdoor use in all weather conditions. I’ll take that a step further to say that the Roam is not design for 24/7 use as an outdoor mounted speaker. Your out-of-the-box thinking as a work-around for an outdoor speaker versus Sonos outdoor speakers by Sonance in theory makes sense; but probably wouldn’t qualify under a warranty claim if your use of the Roam is somehow revealed to Sonos. I won’t tell