Create a comp the same aspect ratio of the face of your building.
Fill that comp with one paragraph of text, all “.” (dots)
Adjust the spacing of the dots and the aspect ratio to match the look you want for the windows.
Apply a “Animate In” / “Random Fade Up” preset (Text presets) and adjust the range, adding some intermediary keyframes to pause the fadeup.
Enjoy results
Tudor “Ted” Jelescu
Senior VFX Artist