I would say that it varies, or can vary, based on what you want to be found. In my opinion of how the setting should be handled, describing or thinking of rooms with lighter damage as well as rooms where there is barely anything left of the furniture or walls gives you and others more variety on what to work with. As for the age of the fire, unless a character is a fire marshall then there's no immediate signs that point to the age of the fire. I'd say it's about 10 years old, though.

Except for the sixth floor, most rooms will be very spacious and/or contain interconnected rooms, so I wouldn't exactly say that it's very much like the sixth floor. Any room or hallway found on the fourth floor would be damaged, though.