finyo, also be prepared that the answers from them may be much the same if you received here. If I called a local US homebuilder and asked how much it would cost to build a house, I'm quite sure they wouldn't just throw a number out on the table. I wouldn't expect them to. As many here have said repeatedly, there are a number of variables to be taken into account.

Well balancing out material and costs labour costs is one thing but 2 story is quite a bit cheaper to build ; far less foundation and roofing area. It also simplifies the plumbing and of course is far more energy effective as downstairs heating will also contribute to upstairs heating. PROs can develop on this. And as Curt points out, modular is a very fast and cost effective solution which can allow you to put your pennies into better quality. Be very careful to select a known and competent professional if you go this way though, i don't know about NZ but europe abounds with cowboys ; low costers are to be strictly avoided.

Debating replacing a 10 degree roof with a 45 degree roof to optomise going off the grid. Building is 9 metres wide [includes 500 eaves] by 12 metres long. We would increase the length to 16 metres to cover an existing deck with ancient corrugated plastic roof. Question is cost. We have the room to build the roof on site and crane into place otherwise make it offsite. We would need to put a couple of windows in length to give character. We would use dark grey ribbed coloursteel ideally and reclad south and west walls with the same material. Does anyone out there have an opinion?

That looks like a NZ house . and possibly even an ex-State House . They were solidly built ( money wasn't a problem ) . But it would need a builder and some investigation , because there will be studs and power and it may even be load bearing . Back in that era , most water and piping was pretty much straight out and down , but there may be piping for water or sinks or showers or similar . You could buy a $100 door at the demo yeard , or a $2500 masterpiece . Tiy might want a small deck and some stairs , you might want a small roof , you might want something more solid . Then you'll need a door jamb , some framing , then presomably paint and maybe wallpaper , Possibly lino or tiles or carpet . And can you match everything , including the paint tones etc , or will you have to redo a whole wall or even the whole room ? Then theres permits and fees and inspections . I'd suggest you won't get much change out of $10k if basic , maybe $25k if you want to go a bit luxe and/or strike problems . But then again , I'm not a builder -- give one a call .