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.

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.

I'd like to suggest that the most important thing here is more about who is using the room. If It's a child's bedroom use lovely children's curtains - there's so much around and any pattern could pick up the wall and floor colours. If a guest room and not used often I'd suggest a beautiful velvet or good quality Linen and forbid the little ones from going in to that room!!!!!! alternately a blind attached at floor level could be raised or lowered so the view is still there but with privacy from waist height perhaps. Good luck. Bee

Do you have a photo of the front of your home? That usually helps when it comes to colour scheme questions.