It sounds like they have gone for the cubic meter costing,
When you build, some things you know to the exact penny, and some things you don't know until you open up.
The first massive thing, that is where the cost is unpredictable is foundations,
Foundations might be predictable, or as you open up you find a big hole to pour money down,
so if you are asking a builder to an all in price, they are going to price in cover costs.
So if you broke it down and took out the items that are unpredictable and agreed to cover them yourself, the builder would not have to cover their asses,
We did away with this issue years ago,
We pass all saving back to customer, so we don't price, we don't advertise, we are booked well into the future and expanding.
I found client also prefer my methods, it is more efficient , and cost effective for both sides.
I would give you the design and drawings, the planning negotiations and applications, price of materials , the hourly rate of each crew member, procedure of works, a break down of allocated timings, service costs, trade costs, full project management, high end finish, we have never gone over time,
We work with the client's budget (we have never gone over), we adjust the design to the budget, if we make savings along the way, then the client can either retain it, or re invest it into the project.
I get all fittings, service, trades, gear hire, materials far cheaper than any client will ever be able to, as I put a lot of money through these companies and suppliers each and every week, year in year out, I get everything at least 50% less than the client can, more usually,
my trades come on demand, which means no delays,
Speed quoteing goes a little like this,
bulk standard new affordable living type home, cubic meter £1,000
then up in jumps of £500, as to finish.
work out your cubic meter of your build, divide the quote, and you will work out what they priced in at.