I think the sides should have more details, like more windows?

Looks more like a city or county jail now. Good job. The only thing you might add is a sallyport type of door system so cars and busses, with prisoners in them, can drive in and unload in a secure environment.

I changed the windows from large ones to gridded pattern windows

It's a nice building if you're going to use it for an office or apartment building but, I would suggest making the windows more like just slits. I work in a jail and big windows aren't the way to go. Too easy to break etc.