We need a number that you don't have. We need to do math against reality, not what I call, no offense, Fools Logic.
We need some numbers that are not there. No data capture.
We don't know but we can get very close.
Weight per floor, estimated from gross weight of building. How many floors above, 20 something? Again that is a close guess.
OK, mass of that, in kilograms?
But, terminal velocity depends on two things and not the mass at all. It is shape and width...in this case a flat panel. Easy.
The other thing is the atmospheric density and altitude, humidity even.
So, get numbers, that you like, even rough guess and you will see.
Yommie, free fall and TermV? Same thing.