I agree with keeping kitty in the room with a sign on the door. With my dog I also put a baby gate on the hall side of the doorway. In addition to being a safety stop, it was another reminder that this is NOT the bathroom! I would also recommend starting to use the room a few hours at a time for kitty so he is used to it before the renovations.
I had my upper bath overhauled a couple months ago, a week and a half of construction fun. The fuzzy one (about the same age as yours) was relegated to the basement, with her little litter box and water, when the guys were coming in & out frequently (i.e. demo) or doing loud stuff. She protested LOUDLY, as only a Siamese can.
She did get let out when the crew wasn’t hauling things in & out. The biggest issue was the nosy little bugger trying to help them tile the tub (rolling eyes) We heard “Heeyyy, Kitty” several times from upstairs.
The guys knew I had the cat and were good about keeping the door shut when they were going in and out to cut tile. If nothing else, I didn’t want flies in the house. I didn’t think it was asking much for them to open/close a door while carrying nothing more than a few subway tiles.
If you ever need a crate, get a cat playpen wth benches in it, not a dog crate. Mine is by Midwest Homes for Pets. Cats don’t want to be low on the floor. They like being up on the benches. The playpen is a metal cage on a plastic mobile base. Easy to roll it around. I got padded benches. My cats are very contented in there. They feel secure because of the height. A dog crate with same 24x36 footprint did not work because being “trapped” down low bothered them. Taller playpen does not worry them.
Years ago, then-DH and I DIY-remodeled the upstairs bathroom in our 100-year old farmhouse, which involved ripping up the existing subfloor to level it. That evening, one of our cats went missing for a few hours… Being 100% certain we hadn’t left any doors or windows open, I was freaking out because we could NOT figure out where she went.
Late that night, she reappeared, absolutely COVERED in thick, dark-grey dirt. She was an orange tabby, not that you’d know it to look at her, as she was literally covered nose-to-tail in filth. Turns out, the cat decided to spend a few hours exploring BETWEEN the floors of our house-- she got access thanks to the ripped-up subfloor in the bathroom, and I’m pretty sure she used her own fur to chimney-sweep between each and every floor joist.
We actually had to give her a bath that night. Not my idea of a good time, nor hers I’m sure.
Moral of the story? Kitties plus remodeling do not mix. Proceed with caution!! I think locking your kitty up in the guest room is an EXCELLENT idea.