When the office fitout is complete apply for an occupancy certificate. You cannot occupy the site until you have approval to do so (if it is required).
Undertake a defects inspection. Make your fit out contractor aware of items you are not happy with and set a deadline for them to be rectified that you can both realistically agree to.
Note in order to get your Occupation Certificate amongst the other certificates that will need to be compiled, the NSW Fire Safety Certificate will need to be signed by the building owners, this can take time, especially when Strata is involved.