Section 112 of the Act allows exclusive use of common property under the terms of an agreement approved by special resolution (just like a by-law).
This is probably the simplest solution as the agreement can be attached to the lot (so it transfers with the change of ownership) and would not involve change of ownership or recalculation of levies. It can carry any conditions that either party requires, such as an agreement that the lot owner maintains and repairs the property at their own expense, to a reasonable standard etc etc. The “rent” for the space can be indexed.
Otherwise, the purchase option requires all sorts of hidden extras, such as recalculating levies, taxes, legal fees, and so on.
The value of the purchase should be calculated, at minimum, as the added value to the apartment minus the cost of the work, including legals.
I would say, go for a permanent lease and the best way to achieve this would be to send a letter of intent in which you would lay out what you plan to do and how you plan to do it (with approvals, of course) including a commitment to cover all legal fees and the cost of a general meeting (if required) to pass the special resolution.
And with that in mind, your next call should be to a specialist strata lawyer.