Kia ora

As above, there are a number of free services available, with great step-by-step processes on their website.
I have regularly used employment.govt.nz to build robust contract agreements (whether permanent, fixed term, casual), and it gives you recommendations and options as to which clauses you can choose to leave in or not.
The employment agreement builder is super useful – I hope this helps!
https://eab.business.govt.nz/employmentagreementbuilder/startscreen/

Cheers
Jada