adding unit/s to SP by developing common property

just throwing a curve ball of an idea. 

We live in a 6 unit SP, (NSW) with a decent sized back yard, bigger than most in our area. We have an old brick laundry building that could use some TLC. While investigating what is needed, a light bulb went off in my head. While we need a new roof, why not go up and add some extra housing there?  That might seem like a hair-brained scheme, but i really would not know where to start investigating the possibilities. 

I know other blocks in our street have received council planning for additional units (in additional buildings) – and I guess there was a developer involved there. If the Owners decided it was ok and gave the go ahead, what would be the procedure here? I’m assuming that 75% of owners wouldn’t have an objection. (Probably 5/6 at least) 

Do i discuss with the Strata Manager first? Any idea on lawyer costs? by-law costs? I would be able to fund the building and the development fees, and hopefully own 1 of the units outright. 

What I am thinking is that the new unit/s would be built above the existing laundry space, have separate access to each unit. They would also be smaller than the 6 existing units due to their size. The laundry and storage could be reconfigured and made modern and common property loss would be kept to a minimum. 

I’d really appreciate your thoughts on this. I’m currently looking at having to move on because i can’t make it up 2 flights now and retirement looms. I love our block, have great neighbours and a beautiful garden. It would be great to be able to move out back to a smaller unit with easier access.  

Thank you!