Balcony over the flat top garage

We recently built a house in Donnybrook with Henley Builder, The garage rooftop is flat covered with colorbond sheets. we are thinking to utilise this space for a balcony. One of the windows that has access to the garage roof will be changed to a door. 4 walls of the garage are brick veneer. We are planning to build a decking over the roof, so we will not remove the existing roof, just to build a subframe attached to the building and lay eco decking on the subframe. We already have a wrought iron balustrade the height is 1100mm. Please call us to discuss further. Kind regards Vlora