What is the purpose of that little house structure on top of that 100 year old brick building?

Isn’t that where they keep the pigeons? lol, I have no idea, maybe some kind of old-fashioned water storage?

Roof access?
It is also a flat roof, so maybe it is also a shed to store cleaning tools, for when the roof gets covered in twigs, leaves, muck, and dead birds.

There was an old, very-creepy-looking funeral home in a really bad part of downtown Memphis that had a structure on the roof such as this.

I didn’t know what it was, but it sure excited my imagination. That and some outdoor conveyor system on the side of the building.

I think @ragingloli is probably correct. Roof access makes sense. A flat roof would require access and maintenance.

@Yellowdog Our old building has a metal ladder on the back. Old brick stage theater. @Dutchess You saw our old bldg. No cool little top though.

It was a cool old building @KNOWITALL.

Housing for an elevator motor (so as to not take up space on the top floor/to be able to lift things up to the top floor)?

Or a thermal convection vent, to let warm air escape.

Center staircase, this is roof access at the top.

We have an old building downtown with a much much bigger shack. It is the motor house for the elevator. The building was a Essex car dealership with the service department on the second floor, sales and parts was on the first floor. Elevator is still working, it is 25 feet by 12 feet.

Well, I’ll just pop in there one day and ask them!

Excellent idea. Clearly the structure was an afterthought, built to house some infrastructure development acquired subsequent to the building’s construction.

Yet another possibility is a structure to house a water tank to improve water pressure.

It’s a fancy ventilation vent.

I thought it looked more like a fancy non-ventilation vent.

Some one FB said a tornado dropped a house on it!

Roof access, and maybe an A/C unit. Lots of buildings that predate A/Cs, add them on the roof.

Poorly placed outhouse.

An extra large room for both roof access and more storage.

Could it be a cold air intake for the building’s heating system? (For combustion of heating fuels?)

I dunno! I’ll find out tho!

Are you talking about a gable?

Look at the picture.

Could be roof access to building , equipment room, or where employees are sent for timeout. ;)