Hall-Atwater is only two stories high, so the view isn’t remarkable.
From the roof you can get into the machine rooms. DON’T ENTER IF YOU HAVE LONG HAIR OR LOOSE CLOTHING. Many of the machines have dangerous exposed, rapidly spinning parts.
Also, the machine room leads to another part of the roof that contains a ladder that will take you to a higher level.
Shanklin is a little different: While it’s got more levels than Hall-Atwater, it’s not actually possible to be on the “roof” because it’s sharply sloped (The posts that look like they could be a balcony are just there for decoration). So don’t try it. The view isn’t worth it, anyway.
Finally, there’s the Hall O’Dead Stuff on the 2nd floor in Shanklin: