I’d be interested in this too!
I bought a humidity tester a while back as I was concerned about the humidity here - there’s a river running at the end of the garden and, well, this is Wales - where’s it’s usually damp weather most of the year!
A Raspberry Pi in each room seems like a lot tho… unless it was used for other things too? Such as a home CCTV or other security system, perhaps sensors to activate lights etc?
Or use a single unit and attach to a vehicle that is also controlled by the system, which goes into each room every day to check settings? Now that would be very cool! 