Dear JB
My view is that, without any evidence to the contrary, you will find that the roof space is Common Property. If the previous owner had been granted exclusive use of the space by the Owners Corporation then this would have needed to have been approved as such and recorded in the minutes. Maybe you could enquire from the Secretary of the Owners Corporation as to the history of the “enhancement”.
It may well be that the previous owner carried out this work without any approval and as such you should be careful as to how you use the space. If there is power to the area you should be careful in case the work was not carried out by a licensed electrician and the area may be highly dangerous. If you intend to use the area for storage I would get an electrician to check the wiring. Apart from all that I would be careful of liability issues as if damage is done to the common property you might be personally liable to the Owners Corporation. It doesn’t sound like a good idea to make this “habitable” and I guess you mean for it to be suitable for people to live in your roof space (!).
Hope this is of some assistance.