First off all the slope of the site is really important. If it is steep and you need to put in retaining walls and the expertise of a Geo tec engineer, your house building costs is going to increase by a lot. So always try to choose a flat building site. The next item would be the slab. It is cheaper and better for thermal mass to build your house with a concrete slab on the ground. Not only can you eliminate highly treated timber for footings, but your house will be less drafty and better insulated.
For the external wall I recommend 140mm thick framing if you want a stick framing house. (this system has proven to be the most cost effective for now). Not only can you beef up your insulation value in the wall, but also this wall thickness is needed if you want to have a insulated perimeter foundation. Actually I would now recommend to use SIP panels for the entire house. Please refer to my blog article for more info.
As for the windows/door, I recommend a thermally broken profile. I know it doesn't sound good but it just means the inside and the outside of the frame are not conducting heat. Of course you want to use Double glazing with pref. Low-E and Argon filling.
As for the roof a cheaper option is to go with a truss roof with a flat ceiling. Also a low slope will reduce costs as the builder can run over the roof, easy for the sparky and the plumber and no high walls to line. A bit more expensive option would be to go with Scissor trusses.