The scene is a memorable one because it is the one where Shatter returns to Ti Lung's flat to hideout from the guys trying to kill him and he witnesses Ti Lung putting his kung fu students through their paces on the apartment roof.
Looking west: Sincere Building (still around too) on the right
Looking north: towards Lion Rock
"As for Ti Lung's flat with those Kung Fu scenes, it was Mongkok alright. That's the roof of the building at the south-east corner where Argyle Street meets Fa Yuen Street. The building is called Lee On Building and it still exists. Tai Chi master Cheng Tin Hung used to teach there. After his passing some years ago the Building management would not allow further activities at the roof anymore...The Hong Kong Tai Chi Association is still on 12th Floor though."I must admit I don't know much about Tai Chi or Cheng Tin Hung, but being from the UK and an avid reader of Combat magazine between '86 and '92, Cheng Tin Hung's student Dan Docherty is a name I recognise. Anyway, you can read more about him over on wiki.
It's a nice little link there I think, but I was scratching my head as to how and why Shaws were filming up there until I read that Cheng Tin Hung had been involved as a fight choreographer (and a small cameo at the beginning) in a Shaw's production - The Shadow Boxer - the very same year that Shatter was made. Both films, The Shadow Boxer and Shatter, shared a crew member: Johnston Tsao Chuang-sheng. Incidentally, he also worked on the other Shaw/Hammer co-production The Legend of the 7 Golden Vampires. Anyway, I guess it's not beyond the realms of possibility that the roof was borrowed as a courtesy between friends or recent acquaintances.
So if there are any disciples of Mr Cheng out there who are curious about seeing what their sifu's rooftop used to look like, look no further.
Once again, many thanks to Thomas for filling in the detail that I would never have been able to find.