Both your balcony and the ground below are common property. You will probably need a special resolution by-law which should include a clause saying that you and subsequent owners of the unit will pay for repair and maintenance. You will also need council planning permission.
If your neighbours don’t agree, you could go to the Tribunal seeking an order compelling the owners corporation to approve it.
It’s theoretically possible but I wouldn’t bet my house on it. A better option might be to offer the owners corp money for the use of the common property so they have an incentive to agree.