Even though the windows over are wonderful, the back pocket will feel the cost as they would be custom made, more expensive for the builders to install, but if casements, (open at side) that would make for great windows which catch the breezes, why anyone would want fixed windows is beyond me, the more we can open up a house and naturally ventilate it, the less you have to spend on air con, two angled windows need to be fixed. Any hot air over the opening part will sit in the ceiling space, but if you wanted to be even smarter, then i would consider the roof windows, which pivot and let the house ventilate totally, also like the cost comment with the windows over, these are expensive by it looks like you have the pitched ceiling inside, which would allow for the roof windows.

As said above high ceilings and windows can have issues such as those raised. If this is the only way to get north light in to a living area then you can mitigate some of the heat loss issues using fans which push the hot air back down, or mechanical reticulation systems. High levels windows are great for passive cooling, but unless the warmth of the sunlight can be absorbed by some thermal mass then your not likely to get a huge heating benefit. Alternative design layout which get north light into living areas in a more conventional manner would be more practical and cost effective if you can achieve that.

New question (not referring to original photo) - Thanks for all the suggestions. Just to clarify my post, the original design in black is the original house with a gable roof, and it already has a small extension perpendicular to the main house which has a lower gable roof. (Design from the south is below, yellow = original house from east to west, green = existing extension projecting to the south with gable roof perpendicular to original roof, red = proposal if this is possible, to widen the extension). If we want widen to the extension can you just widen the gable roof or is that a costly nightmare? (I assume we would have to rebuild the roof on the existing extension?). We may be looking at replacing our roof anyway in the next couple of years, so this could all happen at the same time. (Yes, will talk to a building designer too).

Thanks Kate and Amony, We don't have our own engineer. The builder has developed the plans, design and will engage their own engineers through the process. As working drawings haven't been developed yet (awaiting final fixtures / fittings), I'm not sure if we could reasonably engage our own engineer, but let me know if you feel otherwise? We don't have our own architect, the design is a modification of a standard house plan that the builder offers. Noting that they show a cathedral ceiling with glazed gable very close to what we have been shown on their website / marketing material, and what is in our contract. With regards "the builder's drawing is ugly", I assume you're referring to the proposed new design, and yes we certainly agree! Though if you're referring to both original and proposed, then I guess that means you're recommending we don't pay the ~$58K and revert back to a normal ceiling and forego the glazed gable. That is certainly an option we are considering. We agree with respect to "if he was unable to follow the plans, then that should have been conveyed up front", and would have likely not gone with them, hence we feel like this is false advertising / bait & switch and depending on how things we go we will probably report them to the ACCC. With regards "this builder will be a major problem as you continue with a build and will try to cut costs for himself", I can't argue with that, but for the moment we have a signed contract in play. So would your recommendation be to potentially forego the 5% deposit (assuming they quantify their reasonable costs up to this point) and walk away? This is certainly a scenario I am aware of. For "what do you do if he changes plans partway through", this is where we are seeking some external legal (due tomorrow). I feel like the builder is in breach of contract, in which case we should have a way of cancelling the contract without losing our 5%. Right now we feel like they have made a major mistake in selling us on something they feel like they can't actually build, and hopefully legal advice supports that they are in breach.