I need advice. Cockatiel. So Currently there are some men fixing air vents in my apartments restrooms and just found out

Hmm okay. Yes, the fumes can definitely be harmful if they are exposed to a lot or for a prolonged period of time. I have a few suggestions for you. The first is I would definitely not put him outside due to him becoming too cold, the risk of injury or escape. But when they are painting, I would recommend having the bathroom fan run the entire time, as well as the oven fan that should be above your oven. If you have the ability to at least crack the windows (if they are screened) during the day that may be helpful as well. You can also gather a few fans and position them near his cage but facing outwards so the fumes are pushed away from his cage.

Alternatively, if that doesn't seem to help keep the fumes down, You may want to take him to a friend's or family members house for the next day or so while the painting is happening. This is probably the safest option for him.

It may be worthwhile to leave the fans going overnight, especially the bathroom fan and the fan above the oven since that will suck out a lot of the fumes. I would say you can leave the fans on that are by the cage as long as they are pointed AWAY from the cage and are not creating any significant drafts for him. To limit that you may want to cover his cage with a towel or blanket. We don't want him to cool down too much.

I think I would be a bit too worried about leaving him in the car, since it is too hard to predict how hot or cold it can get inside, especially for a bird that is so susceptible to temperature fluctuations.

Are you close with any of your neighbours? Anyone you would feel comfortable bringing the cage over at least during the day or something?

Another option is you may want to contact your building manager and ask if you can keep his cage inside their office in the lobby or something, especially since they didn't tell you ahead of time that they would be painting!

You might want to see how running the fans does and whether that is strong enough to pull out the fumes. Boarding places are an option, but there are risks associated with them too including stress (for both you and him) as well as interaction with other birds that we do not know their health status. One thing you can try also is calling your vet in the morning and seeing if they would be willing to board him or whether one of the staff would be comfortable keeping him for a few days. That way you know he is being well looked after!

I wouldn't be so much worried about long term issues after the painting but more in the immediate future, so keeping a close eye in him, monitoring his breathing and watching for increased respiratory effort, open mouth breathing, panting, tail bobbing, becoming lethargic or anything unusual. if you notice any of those signs immediately remove him from the area. Try to keep his cage in the furthest room away from the bathroom, keep the fans on, and see how he does with that. If you think the fumes are still too strong, a boarding facility may be the safest option in the end.

I hope that is helpful but if you have any more concerns or questions just let me know. You can message me in our same chat here and I will be coming on throughout the weekend as well and can come back to assist you.