eurojim – what you’re proposing could be considered as erecting a new structure on the Common Property (roof and walls), and if that’s the position adopted by your Owners Corporation (O/C) then unless your Plan has a Registered Special By-Law covering that type of construction, then it’s not a matter for consideration by the Executive or Building Management Committees, but rather by all Owners present personally and by proxy at a General Meeting, where ≥75% would need to vote in favour.
The fact that the proposed pergola is on a terrace that’s part of your Lot may confuse how your O/C considers it, but instead of pre-empting how your O/C may or may not react, why not discuss everything with your neighbours prior to finalising your design.
Early discussions will give you the opportunity to explain your plans and to perhaps resolve any issues such as those that you raise with appearance etc, thus reducing the likelihood of opposing votes at the General Meeting if it comes to that, and/or of adverse submissions if consent is refused and you decide to take the matter to Mediation.
You seem inclined to approach this issue sensibly, and in that regard going ahead with your proposed pergola without the prior written consent of your O/C would be ill-advised in my opinion, particularly as your O/C could seek Interim Orders to halt construction, but moreso because IF you do approach things as I’ve suggested you would, again in my opinion, have excellent prospects to successfully overturn any refusal of consent by the O/C under Sect 140 of the NSW Strata Schemes Management Act which amongst other things states at Cl:1 that “an Adjudicator may order an owners corporation to consent to work proposed to be carried out by an owner if the Adjudicator considers that the owners corporation has unreasonably refused its consent and the work relates to any of the following:
(a) alterations to common property directly affecting the owner’s lot”
That sounds very much like your situation to me!
Council involvement depends upon a number of factors, including the size of the pergola where structures <25m2 and <3m high are usually considered Complying Developments, but as your proposed location may be atypical you should personally make, or have your Architect make some discrete inquires with your local Council. Remember though, if Council requires a DA they won’t consider it without a letter of consent or of no objection (as applicable) from your O/C.