Who owns the roof space

A reader we’ll call Emma has sent us the following conundrum:

My question is –

Live in a 5 unit block that happens to be company title. 

When I purchased mine, 16 years ago I was told that the roof area above my unit was also mine and I could go up into the roof if I wished. Could never afford to do so but have happily had it up my sleeve as an excellent selling point when the time comes and would also add a lot of value, having a rather sensational view of the beach from my high spot.

A young couple have since moved in three years ago and tell me that they want to create a storage area in the roof and that the roof is common property.  They have also got the managing agent on side, who is also new and they instigated to get him take over our building.

I know this would apply in a body corporate building but was given to understand by people that used to live here and the people I bought from that it is different in company title building.