When you need a certifier
If you need a construction certificate or a complying development certificate, you need to apply to your council or an accredited certifier. Councils and certifiers issue a range of development certificates.You also need to engage a principal certifying authority before work starts. Your principal certifying authority may be your local council or a certifier— the choice is yours.

Who engages the certifier?
Only the person with the benefit of development consent (usually the property owner) can engage a principal certifying authority, and must sign a written contract with them before any work starts.Your builder is not allowed to do this on your behalf, and you are not obliged to engage a certifier suggested by your builder.Find out what a certifier does http://bpb.nsw.gov.au/certifiers-role/what-certifier-does or read the guide to the building approvals process http://bpb.nsw.gov.au/sites/default/files/public/Finalbuildingappbroch.pdf to understand what you need to do at each stage of construction.