Itsa,
I don't have a Champaca, I have a Figo, but, it is evergreen.
It needs sun.
So, I wouldn't put it in the garage with no sun.
Hope it is alright for you.

It does not go dormant so putting it in a dark area for an extended period of time may kill it. Michelia Champaca cannot survive below freezing like the Michelia Figo (banana shrub) can. So if your garage is not heated it might freeze. I would bring it inside and keep it away from direct heat sources that might dry it out and give it a sunny window. Try not to under or over water it ...checking to make sure the soil is dry an inch down before watering again. If you can give it a mist with a hand sprayer daily it will be helpful in keeping the humidity up. Some people put a saucer under the plant and put some pebbles in the saucer thus raising the plant up a little and putting a little water in the bottom of the saucer. This helps with humidity but prevents the plant from sitting in the water which can lead to root rot. Hope this helps a little :)
~SJN

When people try to manage these as house plants the basic issue they face is that they are dealing with a tree that really wants to be outdoors in a suitable climate or in a greenhouse of enough size to accommodate it - this is not just a tree, it is a tall-growing tree.

They can get large but you can always prune them. Some plants can handle both root and foliage pruning. I have several very tropical trees known to get 20-40 ft (vines too) that I keep pruned so I can cram them into my greenhouse from Dec-first week of March here in zone 9a. During most of the year I sink the pots into the ground. When frost hits (usually December-ish) I dig them up severing the roots and use a handtruck to move them to the gh. Works out pretty well so far. Eventually, I plan to move further south (FL) so I will no longer need a gh because I have way too many plants lol.
When I lived in a colder zone and didn't have a gh I had a ton of houseplants every winter.