just wanting to build a home would want a cost breakdown to unnecessary level of detail.
You don't need it to ensure you are not ripped off, if you shop around then market forces will lead you to the best price for what you want done.
Yes, over the years I have provided detailed cost breakdowns on commercial and government jobs but that was for the purposes of managing progress claims and only after the tender has ben won.
As a builder I would be suspicious of a customer wanting this level of detail (red flags come up) and would simply decline to quote or put extra margin for the perceived risk of dealing with potentially difficult customer.
The customer runs the risk of getting bogged down in detail, loosing the focus of the big picture and risking a blunder. You need to focus your energy on the things that matter.
All you need to do is:
1 Know exactly what you want (and don't change your mind half way through the build)
2 Make sure you can afford it
3 Shop around and find the product you like and compare with competing products, then shortlist
4 Negotiate hard with the preferred builder, making sure they know you are talking to others
5 Make sure you have pre contract review, then independent inspections during your build
Asking for cost breakdown isn't going to put any dollars in your pocket but it could loose you plenty.
With due respect you are completely wrong on this one. And I say this with 25 years experience running construction and development companies.
Getting a cost break down will allow you to compare apples with apples and in fact I would argue that everyone should be getting a cost break down.
for example, if one builder has allowed $3,000 for waterproofing and another has allowed $6000 for waterproofing you can ask why the difference. The cheaper guy might only be allowing 2 coats where the more expensive guy is allowing 3 coats and maybe a better quality product.
As a consumer waterproofing maybe of particular importance to you and having that knowledge gives you more choice. But conversely you may be happy with 2 coats and you can save yourself $3000.
Framing is another key area. One builder might have $50,000 and the other has allowed $80,000. Knowing there is a difference you might find out that the cheaper guy is prefabricating and using 90x35mm and the more expensive guy is cutting onsite and using 90x45mm. Obviously with a huge difference in quality. But if you have a tight budget you will be able to get the $80,000 to reprice the job with prefabricated frames. Knowledge is power
There might also be a huge difference in prelims, one may have allowed for traffic control and cranes and the other not. The cheaper guy might be thinking he can hit you up for a variation later on. Again, having this knowledge can help you minimise variations during the build.
Again, having this knowledge allows you to negotiate and make changes for items that are important or not so important.
As a building expert I am surprised that you arent aware of this? Its actually construction 101