Warranties are expensive and housing is already far too expensive in Australia. We don't need longer warranties.

What we need is workers who actually do their job properly. There's a distinct lack of those in recent years... my advice is don't buy or build a new home. Get an old one and pay for it to be renovated. Supervise the renovation work very closely, and avoid letting them do anything too major.

If your typical family home is meant to last 30 years, the warranty should last 30 years.

The expectation is 60 years. 100 if it's "well built".

However, that isn't 100 years with zero maintenance. You will have to repair things... and that's where the warranty cost becomes an issue.

There will be arguments over what is covered under warranty. Those arguments might be free for the home owner, but they are not free for the builder. Your (or whoever buys the house off you) will complain the gutter rusted out, and the builder will have to hire a scaffold for a few thousand dollars to safely get up to the roof and inspect the gutter, and then tell you it's because you allowed tree to grow over the roof and didn't clean the leaves out of the gutter. They will have to take time off their normal paid work to do all of that and they absolutely will charge upfront on the assumption that they'll be coming back to your house occasionally for the next 30 years.

If you're wiling to pay... then I'm sure you can find an insurance company who will cover it. Won't be cheap though.