Usually, the owners corporation would pass a by-law allowing exclusive use of the courtyard, permission which could only be withdrawn or revoked with the agreement of the owner concerned. The rights conferred by this by-law would pass to subsequent owners of the lot.
The “purchaser” would pay to have the by-law drawn up and would pay the costs of the meeting held to pass it (if it was a separate General Meeting and not just the AGM).
The by-law would state that the owner took over responsibility for the repair and maintenance of the property. It would require a special resolution (75 percent of those voting) to be passed.
The payment to the general fund of the owners corp would be calculated by getting an assessment of the additional value of the property with courtyard etc minus the costs of the work involved, including the French windows (which would also be part of the new by-law).
The benefit of the payment to other owners of a payment to the admin fund would be that this would be less money that they needed to raise through levies – they could even award themselves a levies reduction if the sums were significant enough.
The owner doesn’t need to “own” the courtyard for it to be considered part of their property. Most modern buildings’ balconies are common property but are considered part of lot property when a unit is sold.