Well there isn’t all that many options. The OC simply have to repair and maintain common property as per s62 of the SSMA. If you don’t have a sinking fund plan there isn’t much that can be done about that now in hindsight (apart from starting a 10 year fund plan).
However if you don’t have enough money in either the sinking or admin fund and the repairs need to be done ASAP, then you will need to call a general meeting to raise a special levy to cover the costs of the repairs. However before you raise the special levy, it would be a good idea to get at least 3 quotes to put forward on the agenda of the general meeting and have the OC decide which quote to accept.