Well, this is the ideal time of year to do them isn't it? Problem is being there when it's dark - and then finding a decent line up of a/c. Standing on the roof of MAN T1 in the dark in a freezing gale for a few hours isn't my idea of great fun. (Though I suppose I could photograph whatever's there, then go downstairs and have a drink and a burger, then back up an hour later when it's changed...)
How about LGW? Or do they close the terrace when it goes dark?