How to treat for cockroaches in apt building?

Unless management treats the whole building you are likely to be dealing with roaches all the time. What ever treatment you use will only be temporary because they are still in the building. To be effective you have to rid the whole building

Go to a Gardening Store I guess or HOME DEPOT and ask for Diatomaceous Earth. It is a special type of dirt, that is made up of tiny sea creature shells. This you spread around the water heater area and leave it thick on the floor.

DE gets into the cracks of the shell of the bugs (and like if you chewed on a mouthfull of glass, the shell will cut them up good...and they die.) Which is what you want, right? Make sure no one else cleans up the dry dirt you laid out on the floor as it is an area confined to you, no one else should bother it. It can be reused over and over so is never tossed out...just some of it is disbursed to another spot should that be necessary. Slow but sure that should stop the bugs.

We had a problem with the little ones, after moving into a small apartment on a ground floor that had been vacant a good while. They were worse in the bathroom and kitchen. I got them under control with a gel bait I found on Amazon, Syngenta Advion. Not sure if they can/will ship it to just anywhere; there could be restrictions. And, on a side note, when trying to store the leftover gel, it smelled horrendous. But, it did work.

Roaches are not tiny unless they are babies, so you are seeing baby roaches. Roaches can develop resistance to poisons. Have you ever seen any roaches that are white or lighter colored? Those have developed resistance to the poison being used. In apartments, these bugs travel between the apartments through shared vents, electrical outlets, holes used for plumbing etc. No way to keep your apartment roach free if your neighbors are pigs.