It depends on many factors, some interrelated, some not. Unless you are dealing with more off the shelf/volume/standardised design solutions I'd be somewhat wary of utilising any fixed overall /m2 calculations to base your decisions on what you can or can't achieve or should/shouldn't do for your project :) We prefer to present/offer our professional opinions of likely construction cost by collating the projected likely trade breakdowns carefully considered for each particular scenario proposed, factoring in various aspects such as quality, site, scale etc that will ultimately contribute to influencing the number involved. Have found this to be a more accurate/realistic approach than simply applying $$/m2

We too are about to build though picked a project home builder because of the 'volume build' cost savings. But we are making modifications to better meet our needs. Our initial plan was heavily customised and came in around $150k over what we wanted, but that was highly spec'ed insulation with double glazed windows, cathedral ceiling, very large rooms, 2 bedrooms with ensuites plus another bathroom and toilet, plus another 2 bedrooms, large undercover alfresco, very complicated roof line (apparently that really adds to the cost)... so we learnt a lot of lessons from that. We have scaled back the size of rooms, gone for a simple shape/roofline and will add character through textures (timber panelled walls, etc), some of which can be added later. We have maintained top notch double glazed windows and high R factor insulation (Southern Highlands location, so you pay either way if you get that wrong.. up front or in excessive heating and cooling bills), but cut back to only 1 bifold door and embraced good old double and triple panel sliders - a huge cost saving in itself. Would also love a cathedral ceiling but may need to lower our expectations there. I have to agree that a price starting with a 3 at the front - or even a 4 - does not seem at all realistic for that house. If $360K is breaking the bank, you really need to think about how you can meet your needs in a different way. I'd start with design... would a 2 storey home offer cost savings? Less roof for the same floor price? What about attic bedrooms and/or an attic activity room? I don't think attic rooms are actually that cheap, because of the need to strengthen the floor/ceiling, but it would be good to ask. Do all the children need a separate bedroom? If there's a significant age difference between eldest and youngest, you may find you can get away with younger siblings sharing for a while longer; perhaps even till an older child heads off to Uni?? Think of all the materials you will be chosing and the impact those will have on your home. Number and type of windows, floor coverings, tiling etc. I don't feel your rooms are overly large, but agree the large Media and Activity rooms are expensive choices. Personally I'd keep one dual purpose room, mainly with the kids in mind and smaller than either of those. You really only need kids tv and computer games out of the family room/lounge, don't you? The scullery and parts of the Master suite are large and the bathroom between Bed 4 and Bed 5 is a waste. I'd put Bathroom 1 - with the only bath in the house - and the loo side by side and accessible from near the kitchen area. I've seen some homes with a 3rd toilet in a large laundry, which can be handy with a horde of kids around. On a different note, that laundry seems way too small for a family of 6. You want those teens doing their own washing and ironing ASAP... they'll need room to do that. And you don't want to skimp on windows, insulation and eaves that suit your climate - they can really help to reduce your home's running costs. Re the vergola suggestion, I'd steer clear of that. They are costly, not really water proof and don't age well in my experience. A few friends have installed them and all have shown 'buyers remorse' quite quickly. An under-roof alfresco is pretty nice to have, but even a solidly built pergola with a simple sun/rainproof roof is nice too. As for the cathedral ceiling, I LOVE it. Opens a house up beautifully. A half cathedral (that's not the right term but i hope you know what I mean) may reduce costs a little. Otherwise, use your windows to maximise light (but not heat), raise the ceiling heights throughout the house to 2.7 (it's usually fairly cost effective to do that) and ditch the cathedral ceiling. Good luck with it. It's an exciting project.

HI All - for some reason my lengthy reply a few minutes ago was deleted :-(. I put so much thought into it! So here it goes again. Basically a big thank you to you Houzzers. MB your subfloor ventilation sounds great and Im glad it's fixing the problem so simply. The reason why Im trying for a whirligig solution is that I favour a passive system, however if it doesn't work I'll look into what you suggest Siriuskey - yes to some kind of kit. I've already contacted a guy on Gumtree selling grannykit frames - he says for something to my specifications would be about $4000 for the steel frame alone. Would need to check engineering details - and the liveable sheds you've linked me to seem to have that all checked. Although getting a local Chippie to frame it all up on site - as Twos Co suggests - is probably the most economical option Two's Co - thanks for the feedback and the excellent checklist of processes. I've covered most of the concerns though - I've got the DA based on my own flimsy plans. Because it's relatively small, I was going to work with the builder directly and over-engineer it. I've since engaged an architect to do some handsketches and draft specs, which will be signed off by a structural engineer. It's basically a portal frame independent structure, with a 3 degree pitch skillion roof. The house was rewired and the wires you can see are non-live looms waiting for the extension! The sewer is not connected and that part was never plumbed in. There's good rear lane access, but for the purposes of getting concrete in, I'll most likely get a concrete pump from the front of the house - for $180 per hour they will save time and make the concreting much easier. The existing trench I got dug in because I had an excavator on site installing those lovely large concrete blocks you can see, for the retaining wall (500kg each). But that was 7 weeks ago, and the excavation has got too large, and I worked out for a very similar cost I can make the extension 1m wider, so why not. The existing trench I can fill in with the demolition rubble, compact, and filled with any fill waste. Two's Company, I'm on the fence about removing the existing Bedroom 3. If I thought it wouldn't add to the costs too much, I'd do it. One advantage is that I could then make the whole 9m long extension (Option 2) around 150 - 300mm higher, (ie a step up from the existing house) and thus avoid too much excavation and a potential pond. To answer your question about damp and moisture, the whole house is facing a hill with 7 degree slope, and fixing this has been the main aim of the retaining wall, however the runoff is only likely to increase in coming years. anyway here are a few photos. The site is still so messy because the demolition only happened 2 days ago - Im still tidying up....

Marble is a unique metamorphic product which forms over 1000’s in nature, porcelain is a man made printed tile product which offers a lot of benefits that a natural product wouldn’t, such as warranty. You can’t scratch off the print on marble as it is the actual composition of the stone which produces that colour where as porcelain printed and mimics this look well. It’s all about what you are after and as long as it is being sealed as required and cleaned won’t give you any issues.