Hello,
You, as a businessman, should know that in price calculation there is a difference between pure trading of goods and manufacturing industry. Your cost accounting is set way too low. It should include material purchase, production, and profit; possibly discounts/cash discounts. Apart from the fact that these costs vary nationwide.
That is why I took unit prices as final prices, which were given to me by a construction company.
Example: I just had the contract documents of a renowned provider from NRW on my desk for review. With 11.80 x 11.80 m and single-story construction, DN 38°, widening the house by 0.20 m to 12.00 m costs €11,400.00.
I hope you informed your client that he is about to be ripped off badly here?
In my opinion, you are under the mistaken assumption that _your_ taste applies to all builders. Not every builder likes straight walls, not everyone likes slopes. In this respect, it is pointless to write about taste and thus alleged added values; that means something different to every person.
So to pick up the current topic again. In building areas here, where much or everything is allowed, roof slopes are almost never built. Either two full floors without slopes or a bungalow without slopes. Roof slopes are almost only built where they have to be built. As has been shown here several times, you hardly save any money by using a few bricks less and if dormer gables or similar are added, it may even become more expensive.
Likewise, hardly anyone builds a flat roof if they don’t have to, at least not here, where it is often permitted. The hipped roof is the favorite, but there are also building areas where flat roofs are mandatory and well, they often look poor. It must be said that the houses are often just blocks without roofs and not such elegant Bauhaus-like projects with projections, recesses, terraces, color design, etc.