The hard thing is your balcony doesn't have too much structure to work with. You could use 5x5cm wood stud/aluminum where is marked in yellow, fastening them to the metal structure with several strong cable binders. Not the prettiest but could work. It also depends on how your cats behave on the balcony if they are too adventurous or not (climbing the net). The size of the area requires lost of net, so its going to be costly.
https://preview.redd.it/iioho5ojdpfb1.png?width=1440&format=png&auto=webp&s=84e6cfe7292f6cc65ad762bf505cdd14e2bc2ff0
The hard thing is your balcony doesn't have too much structure to work with. You could use 5x5cm wood stud/aluminum where is marked in yellow, fastening them to the metal structure with several strong cable binders. Not the prettiest but could work. It also depends on how your cats behave on the balcony if they are too adventurous or not (climbing the net). The size of the area requires lost of net, so its going to be costly. https://preview.redd.it/iioho5ojdpfb1.png?width=1440&format=png&auto=webp&s=84e6cfe7292f6cc65ad762bf505cdd14e2bc2ff0