Strata Monkey – no matter whether your possible use of the Common Property is by way of an exclusive-use privilege or by the purchase of that, in NSW the decision one way or the other must be made by way of a vote on a Motion by those present (including proxies) at a General Meeting of the Owners Corporation (O/C).
A purchase of Common Property (an conversely a sale of it by the O/C) requires a unanimous vote, and the granting of an exclusive-use privilege over it requires a decision in favour by ≥75% of those voting as determined from the units-of-entitlement of their lots (i.e. a “special resolution” by way of a “poll vote”).
Both options would require an adjustment to your Lot’s “market value” to be professionally determined at your cost so that its units-of-entitlement and therefore your Levy Contributions could be also adjusted (⇑) in the case of a purchase, and as the basis of a possibly equivalent annual payment to the O/C to account for the “benefit” derived from an exclusive-use privilege.
A purchase would additionally necessitate at your cost the re-drawing the Strata Title Plan to enable a Strata Sub-Division to be Registered with NSW Land & Property Information (incorporating the former Land Titles Office), whereas the exclusive-use option would require at your cost the drafting, lodgement, and Registration of a Special By-Law setting out the nature of that use and the Conditions arising, including a mandatory one making you and subsequent Owners of your Lot (and not the O/C) entirely responsible for all on-going repairs and maintenance of the area, and typically one requiring the payment of an annual fee to account for that “benefit” arising.
A purchase of the Common Property makes it part of your Lot and therefore yours and that of subsequent Owner/s, and an exclusive-use privilege cannot be rescinded by the O/C without the prior written consent of you and subsequent Owner/s.
So as Peter observed it’s much in a muchness really, and issues around the certainty or perhaps the comfort of “ownership” as opposed to permitted use by way of “privilege” aside, the exclusive-use option is the easier and lesser-cost option.