Here is my experience with hot tubs or swimming pools indoors.
I rented one home with a sunroom and hot tub.
We had to keep the cover on it constantly to keep the moisture from dripping off the glass and wood structure.
The repairs to the wood framing were a few thousand dollars.
We looked at another indoor hot tub rental,
it was downstairs in the basement, the whole house smelled of chlorine.
Most hot tub rooms will have water dripping from the ceiling.
To keep the air dry, you need an air to air heat exchanger.
Otherwise, the cold air coming will condense the water vapor.
Street of Dreams home near Bear Creek.
This one had a swimming pool.
The drywall kept falling off the ceiling.
The contractor tried several ventilation systems,
Problem was never solved as far as I know.
Customer with indoor hot tub,
This couple had a baseball field in their back yard in the city.
That's how big their lot was. I thought it was a city park.
They got so tired of fixing the house, that they sold it and moved to Pullman.
Hot tubs are big water vapor producers.
Have you ever swam at a public pool, and it feels like rain inside?
That's all the moisture from the air, hitting the cooler ceiling and condensing into water.
I can't think of too many public pools that still have wood structures over them anymore.
Best method?
Figure out how to remove the moisture.
A roof seems fine, I'm not so hot on the "closing it in" part.
When I go to Whistler Blackcomb and stay at the Crystal Inn, I use their outdoor swimming pool and hot tub.
The temperature is below freezing, and it feels fine.
The swimming pool and hot tub are on the left, on the first floor roof.
Yes, that's snow on the ground too. It snowed every night.