what documents do you require to prove u r a permanent resident of New Zealand?

Answer 1

A visa stamp on your passport is generally good enough at customs.

The issue really isn't one of documentation. Either you are a permanent resident or you are not. Immigration services keep an electronic register of residents which cross references against passport numbers, so the issue is generally one of proof of identity.

Answer 2

When you are granted leave to reside in NZ as a permanent residence, I would expect that you would receive an official government document of some sort, and possibly a security card with your photo & personal details on it.