We are in the same situation as yourself. We ended up doing 2.5m basement, 3m ground floor and 2.7m top floor with .3m in between the floors as we also had height restrictions on what we could build. We are also building with slope to our land. Our basement has garages, games room and a bedroom in it and we felt that 2.5 worked. Hope this helps.

You should also consider thermal efficiency and your views. Even double-glazed windows transmit heat. Your house doesn't seem to have many eaves. If you have the taller windows on your side facing walls will it mean you just get a better view of the neighbours roof and your side fence? Will they get a better view into your side facing windows? Don't just consider how it looks from the inside, but think about the whole house from the outside as well - including views, privacy, and extra heat gain in summer, and heat loss in winter, plus all of those extra window furnishings. If you are getting custom made window furnishings then there will be extra cost in materials and labour. If you are buying standard off the-shelf window coverings then there is much less range available at 2700mm heights for full length windows. Best of luck, Dr Retro of Dr Retro House Calls

Thanks all for your advice. Ive included some renders that I made with view along the corridor with and without the bulkhead. I don't think renderst does it justice until you actual walk through @ frame stage. I agree that ceiling height and comfort and look, depends on climate, orientation, insulation, relative proportions of other parts such as windows/doors. Because of the Melbourne climate, we have planned for double glazing, and good insulation with R2.5 batts wall, R6.0 ceiling. We have 2.4m height of windows and door around the ground floor which is btw 3 to 3.6m so I think proportion wise should be ok. In the family where it was always planned 3.6m from the start, we have a band of clerestory windows too. We have decided not to be too excessive with windows ( ie 3m and even 3.6m floor to ceiling - how grand would have that looked though! ) to minimise heat loss during winter. Energy rating for house is 7 stars so far. Thanks for giving me the pro and cons - I have some more confidence to let it stay at 3.6m throughout now.

1800mm on a 2740 ceiling height is small. What height, off the floor level, are you starting your 1800mm windows? If you started them at 500mm from floor level, this would give you are nice high window. It would be the cost of the extra wall from floor level. weigh this cost against a 2057mm window. I have 2740mm ceilings and all my living windows are stacker doors at 2340mm. If you are having curtains, you could have your 1800 windows, and have the curtain drop from the cornice of the 2740 ceiling height. This would disguise the low window. But then this also would be an extra cost for the length of the curtain.