I would use 2 x 8 meters Universal beams at the bottom, only 4 meters will be for my building and the other 4 meter will go into the existing building, to help the beams counter react like a seesaw for example. I will be suing c-joists in between the beams so i can place a floor for people to walk on.
In this model I have showed the steel wire (black string) connecting from the front of beam to the inside of existing upper floor. This was one aspect I will change later as it will be very difficult to get the steel wire to go through the glass to the floor, if there was to be any movement this could damage or shatter the glass. I did think about creating two holes on each side of the glass above - however there could be leaks in the future and would require a lot of maintenance. So i will take it around the side of the building going straight to the roof using two pulley systems which will be connected to the existing roof.