Pretty much any structure still needs to meet the building code, whether or not you need a consent. This doc will give you an idea of what you can/can't do without a consent, what you do with it is up to you... :D
https://www.building.govt.nz/project...ilding-consent
If you need some bedtime reading to put you to sleep, this doc explains the objectives of the various provisions to the building code. I wouldn't recommend reading it in detail unless you are an insomniac, but the headings might be useful as prompts to think about what you need. https://www.building.govt.nz/buildin...-code-handbook
And this doc, which used to have to pay for is now free, will tell you how to build a compliant timber framed building - ok if you are reasonably technically minded, but not for everyone.
https://www.building.govt.nz/buildin...amed-buildings
I thin the main things to think about which may not be at the front of people's minds is bracing (for wind/earthquake - floor, walls, roof), wind uplift on roof (they tend to act like an aeroplane wing and want to lift off!) and often missed, internal moisture (even with just a couple of folks sleeping inside, can get damp - potentially cause rot, black mold, etc).
Internal moisture, key is to keep your insulation dry, and good ventilation. A fire helps too. Preferably one that stays in the fireplace... :D Tin walls are cheap and durable, but also good at getting dew on the inside. Vertical corrugate helps provide an air gap and building paper to keep the tin off the insulation. Lining with ply can double as providing the bracing for the walls. That'll do for now.
oh, except this could be the most useful... https://bconstructive.co.nz/sites/de...NT%2012936.pdf