You don’t have to go directly to the top of the building from where the zipline starts.
The meeting point is at the Dubai Marina Mall and you are then transferred by minibus to the zipline starting point.
To reach the Mall, you have several options:
By subway (M1 line) down to DMCC Metro Station + 10-minutes walk
By tram to Dubai Marina Mall Station 4
By bus – Bus no. 8 to the “Marina Promenade” stop + 10-minutes walk
By taxi.