There is so much wrong with the question. Probably more concerning are the builders who will answer the question without a second thought. I too, often get asked this question for which I often reply how long is a piece of string? The reason I am so blunt with my answer is that like so many detailed services or products there is too little information to provide an accurate estimate.
Those in the market to build a house or development need to be wary of such blunt rates being quoted to them by rogue builders. I often say, builders who are quoting per square or per square meter without a second thought should be avoided, no matter the rate they are suggesting. Only the most complacent of builders will quote with such estimating complacency. This has the potential to quickly expose both themselves and the client when the actual cost to complete is north of their vague estimate.
Of course, I do have an average cost. This is not to be mistaken with a rate that I can confidently give any one client. Every house and development is a different beast with large variances depending on the nature, finish, access and scale of the home or development. I would never use my average cost to complete a project as a rate to apply to a client’s home.
So how do you know how much your project will cost without committing serious resources to that project? In truth, you need to consider approaching an experienced builder or estimator who will be able to, using the information they have at hand including things such as engineering drawings if available, to provide an indicative cost to complete. Builders and estimators will use their expertise and understanding of the project to provide an estimate to construct that takes into consideration every aspect of the build including site conditions, level of finish, potential environmental issues and other important aspects of the build. It is always a good idea to invest in an estimator who can provide at a fee a detailed cost to construct with a trade breakdown. These estimates can too be used to keep builders that you wish to approach honest and provides peace of mind knowing the estimator has no conflict of interest.
It is also important you remain engaged with your architect and engineer who will have a good idea of how much your project will cost. This will help to reduce the possibility of designing something over your budget. Builders and estimators will be better placed to price a project with more documentation at hand including energy reports, engineering documentation, architectural town planning drawings and working drawings, soil report, council information and other important information required to accurately price the project.
In summary, every house and every project is different. It is important you consider your budget early and consult with your building practitioners to ensure you design a project that is suitable. Once that is decided, always invest in detailed, consistent and co-ordinated documentation which your builder and/or estimator can then use to accurately cost your project. Lastly, unless you enjoy gambling and losing, never take the word of a builder who blindly offers a per square or per square metre rate to construct your house or development.