That level of fit and finish takes exceptional attention to detail by several trades. Not many tradespeople can do that these days, or at least not the people I've hired recently!

This is a 8m budget 9000sqft new build project (my client’s house)... so I’m expecting we should be able to buy this detail but instead I was told it’s not possible 🤦🏻‍♀️

it's absolutely possible.

I had to build a 10' radius Corian ceiling trim molding several years ago. No way was I going to template some wonky rough-in, so I provided perfect curved plywood plates to the framers.

Day of install, my molding fit perfectly; no template. It had to; it's math.

Get out your checkbook, no bidding here. We old farts who know how to do this stuff can be bribed out of retirement.

That is $889/sq.ft which in some parts of the country still won't be enough to get you that level of detail. I know you wouldn't get it in Los Angeles.

It sounds like you picked the wrong builder. These details should have been part of the specifications and bid documents. Your architect should have recommended a builder that could execute the details that your boss/client wanted in the house.

The budget is fluid and we only need four walls to have this specific detail. We took over the design at the drywall stage so yes we are trying to rescue the house that has been poorly designed by others. Can’t change the builder now but just want to see if there’s a trick to do this so we can bring it to the builder and get them to do the job or hire the right trades to get the job done 🤷🏻‍♀️

If you are in Los Angeles I can recommend 2 contractors that are detail and customer oriented!

The fact that you are asking these questions here, make it look like there is no one with experience and/or control managing this project. There needs to be someone in charge ... and it shouldn't be the builder! Are you willing to tear down walls and rebuild to the correct specifications? You need to have an architect or experienced designer produce detailed plans and specifications for the kitchen and tell the builder to bring in the right trades to make it happen. Tell the builder that "cannot be done" or "we've done it this way for 30 years" are not acceptable answers. Does the builder know you are willing to pay up to get those results?

Who is doing the kitchen design and cabinets? If you are buying cabinets that tend to get installed in modern homes with this look, then that cabinet shop should have connections to contractors that are able to put that look together.

Or find local real estate listing with similar kitchens and find out who was the architect, designer and builder. Make some calls and get some referrals.

Time & materials.

Flush and/or recessed drywall details end up getting installed by finish carpenters in the same way that trim is installed so it will be plumb & square, then drywall finishers can clean it up. Your cabinets have a small reveal. There should be some cabinet makers in your region that are familiar and competent.

There is a high end hidden hinge door shop in your region that would be familiar w competent locals.

Thanks for the feedback 🙏🏽money is not an issue in order to get the look we want. We are doing three Italian Boffi kitchens in this house and the specific details required are to work with Boffi’s products. We don’t necessarily need the reveal. Can absolutely live without it.
Because we are ordering cabinets from Italy meaning that the builder and his trades need to work with products and make the details happen.

You are somewhat accurate. The entire project was inflated in costs with multiple parities getting major kickbacks. (Include the architectural designer, previous interior designer, and colluding trades like the millworker and other suppliers)
The original local millwork was more expensive than Boffi and cannot anywhere compare to Boffi’s quality. So we got rid off those. We are redoing a bunch of details, reordering finishes, reordering doors, and whole other things. When I say the costs is not an issue because it is not, for this particular details we only need them to do four walls that require flush finishes. All the other areas are forgiving.
I know what’s wrong, we came in to rescue a disastrous project and sometimes that is just life. The builder is just a general contractor, they are not that superior but they can always hire better trades that know what they are doing. My goal for this post is really to help me understand how this can be achieved so that I can shut the reluctant builder up and get them to make it happen. 😅

"and he is saying it cannot be done since the walls are never straight."

What the builder is telling you is it is beyond his capabilities to do this type of work. Were it easy and simple everyone would be doing it.

Fire the “builder” and hire the right GC. You can’t take a guy used to caulk and paint hiding his sins and confront them with a naked unadorned wall. If you don’t find the right contractor for this, it’s doomed. Sows ears do not become silk purses. This is a whole lot more than “just” 4 walls, and it can’t be taught over the internet. If you don’t know the right architect, or the right contractor, or have the right trade connections, and can’t draw the right section details, then ......