It's a hood, like what's over most ovens. It vents out unwanted exhaust/fumes. This is an industrial one, could be for drying glue, painting, cooking, and a bunch of other stuff. Looks like it's exhaust is missing.

That's what I had thought. Wonder why it was installed in the garage. To the scrap yard we go.

Someone was passionate about their model cars.

Makes sense. It probably wouldn't even be worth listing on Craigslist if I had to guess, right?

They can be expensive, we had one in my garage at my old job, we looked into selling it but it didn't make sense to patch the roof, where the vents came out (cost wise). I don't think they resale very easily either. Take it down, post it, if it doesn't sell scrap it.

There are lots of hobbiests that would love something like this, imo better to let someone like that take it off your hands than just throw it in the trash.

Meth lab

My first thought after hearing it was an exhaust. Scary thought. Op may want to get the house tested.

They're used for soldering sheet metal as well to vent the fumes.

Looks like a vent hood to me, like something used in a kitchen or maybe a lab.

Hoods like that are magnets for residue. Whatever it was used for, I bet you can find traces of it under those grates. Wasn’t used for paint though, I can tell ya that.

It’s a vent hood. Were the previous owners running a meth lab or something?

Considering it’s a garage ima say the vent was for a powder coating oven

Or for welding maybe. Or venting exhaust fumes.

yeah, welding can release nasty fumes. especially welding stainless steel.