Design and Building Practitioners working on class 2 buildings or buildings with a class 2 part need to register. You must be registered to declare certain designs or building work, and lodge documents on the NSW Planning Portal.
This affects you if you meet ALL of these requirements:

• you are a Design or Building Practitioner in one or more of these classes; and
• you meet the eligibility requirements; and
• you are working on a class 2 building or building with a class 2 part; and
• you are the practitioner who will declare or lodge documents.

Both individuals and organisations can register as Design, Principal Design or Building Practitioner under the Compliance Declaration Scheme. Find out more about body corporate registration.
Registration lasts one, three or five years from the date you lodge your application onto Service NSW.

For more information - READ HERE 

If you are planning the major renovation, new build or sometimes just a small alteration - the cost of approval is very similar. Design & drawings are just the beginning. There is lots more paperwork required than most people realise. I always advise - be prepared to spend between $20k-$35k on the reports and government fees and charges  before you even start the renovation. 
Below is a breakdown of fees and charges for the  DA + Construction Certificate approval for the average alteration & addition in Northern Beaches Council.  ​​
Please note - if your property is located in the hazard zone - you will require the reports prepared and signed off by others. Also note, that some fees and charges are percentage of the building work. 

I recommend to read the blog already prepared and posted by Custom Construction - high end Northern Beaches builder. It will give you a good idea on how to budget for the renovation ....CLICK HERE