Insulate binder roof / attic yourself

Hello, we are currently in the exploratory phase and are checking various BU and GU. One of them, without us asking, directly suggested insulating the attic of the [Binderdach] ourselves. It is not a problem from a craftsmanship perspective, but is something like this unnecessarily complicated, so that he intentionally wants to delegate it? Or is it a well-meaning suggestion?

Google how a [Binderdach] is constructed.
It is simply much harder to access, he will not be keen on that.
The [Binderdach] costs him a good deal less. Keep that in mind when comparing prices.

He explained it like this: you just put insulation wool on and lay chipboards on top. What only confuses me is that he suggested it on his own. Or is there something special to consider with a [binderdach] that is why he wanted to transfer it directly?

That's true. But first, get a proper grasp on it.

I'll try to explain it like this:
Act 1
The house needs some kind of lid so that rain doesn’t get inside. The typical representative of the species "clueless builder" has at most an idea and opinion about the outer shape of the roof when no living space is to be created in the attic. This requirement is attempted to be fulfilled by the contractor as cheaply as possible, because what even the most clueless person easily understands is the number at the bottom line – you get the decision "thumbs up or down".
Act 2
The building regulation "Energy Saving Ordinance" says the house must have a "thermal envelope" (boundary between heated interior and weather-exposed exterior). This has to be somewhere, in the case of the cheapest lid over the top floor ceiling.
Act 3
Unfortunately, at this point the creation of the state required by the building regulation and verifiable by the building authority for conformity between plan and reality is associated with tedious hard work, whose labor costs can easily "overcompensate" the choice of the cheapest design (as they say in fancy language).
Act 4
Here the magic word "own contribution" comes into play: nowhere else can the cat be so gladly encouraged to bite its own tail as here. Similarities between the proverbial cat and the "price-conscious" clueless builder are pure coincidence and entirely made up. However, I do not guarantee the truthfulness of the last statement :)

Hello, we are currently in the discovery phase and are checking out various general contractors and construction managers.

You are brand new and fresh here and maybe should catch up by giving the scrutinizing eyes of the local lions your house design ready for price inquiry (?)

3rd Act
Unfortunately, at this point, producing the condition required by the building regulations and verifiable by the building authority for conformity between plan and reality is associated with arduous toil, the labor costs of which can easily "overcompensate" for choosing the cheapest construction (as they say in euphemistic language).

So is it a damn hard job to install insulation wool up there?

I know what a binder roof is, what its advantages and disadvantages are, etc. But I couldn’t quite imagine that insulating up there is probably a very elaborate job. Hence the maybe somewhat "stupid" question ;)