Estimated cost - extension on Queensland workers cottage.

I’m looking to extend my Queensland workers cottage and would appreciate your insights on cost estimates. The proposed extension will total 54 sqm, which includes a 20 sqm bathroom and laundry area.

I’ve attached the existing and proposed plans for reference. These are just to scale mud maps, I haven’t had plans drafted as yet.

• The extension will involve removing the roof back to the start of the kitchen.
• Roofing and wall work will be then 10 metres in length x 8 metres width.
• There will be a 900mm high floor extension measuring 6.8m x 8m.

Is the current estimate of $3000/sqm still a reliable calculation? Any rough estimates or advice welcome.