I really don't see an issue with the rooflines. Looks like the angles are fairly similar and the clean lines of both structures should be easy to coordinate, especially in your open, rural setting. Since you've found a stunning deal, I would say, go for it! I definitely would want to find an architect ASAP and by all means, before you pour the slab, make sure you have a plan to coordinate.

Thanks for the replies! My wife suggested we talk to a local real estate agent, so i think that is a good idea... just that Im not sure how helpful they are likely to be if we arent selling yet :) As for saving for our dream house, I dont disagree, however if doing this up nicely over the next ~5 years or so while we live here nets us some extra in the eventual sale, then that of course will help us as well. Interesting thing happened today actually. I got a knock on the door and one of the older neighbours asked if he could take some lemons from the tree. I of course said yes. Anyway he was telling me he had lived in the street for 40 years. I asked him if the house had always looked like this, and he said no that ~30 years ago the old old owner did a massive renovation and pulled off the timber and put up the bricks and gutted the inside of the house. Interesting stuff!

It's great to see professionals consider sustainable options

We are also building in Christchurch :) So also had to look at these kind of requirements for sun, but we had a much smaller section to work with (800sqm). If cost is OK ideally a 2 story would get light into more of the rooms. You also saod the street frontage is 35m but the plans say currently the width of the house is only 15m, so you could run more of the house along the frontage to get it aligned with North. Its a big section are you setting it very far back from the street? Or are you worried about privacy? Is there a view Northwards, otherwise if you can set back from the street and add hedging or plantings to increase privacy I would try and align as much of the living space to get the North and west sun. Depending on what your roof is like you could also add a clerestory to get light towards the back - we are using skylights as well for our back hall and bathrooms to make sure they get as much natural light as possible.