Eh, Brane, another tough expert?.
First, in the attic I have everything possible, including the putty that's only for tiles (there are many for different installation locations, loads and types of ceramics, stone when laying), which I laid.
Secondly, Velux window installation prices range from 80 to 90 eur, with installers having their own calculation on window purchase, offering the customer the window a measly 10 eur cheaper than retail at Obnova or Mix, with the difference in their favor on taxation lower by 13%. Installing such a window under normal installation conditions in the roof really isn't rocket science if you read the instructions, stick to the lines and master tool work.
For usual smaller roof pitches, both anchor hangers and direct ones are used, and you finish the ceiling at a height suitable for available attic height, at mine it'll be just 18cm Unifit above-standard 035 insulation, which Knauf Insulation advisors also confirmed is plenty. Anchor hangers I didn't take because I stuffed the semi-permeable foil on the battens. Regarding joints of the final vapor barrier foil, it's all clear to me too - tape all joints together, which still awaits me. I don't know where you builders see the problem in such simple work as attic apartments.
Compared to wiring control units of hydronic systems, where there are hundreds of conductors to first label and connect all correctly per plan, these building processes are pure routine comparatively, sometimes hard to grasp something, otherwise all child's play, I almost sleep next to it when building. All goes by one learned pattern, and if you do more of it, you gain eye-measure like Bosnian building masters have. Then you're competitively fast and relatively quality too, thus earn more time-wise.
Overall, I also had a check by a Bosnian colleague who daily does practically all construction work on site and as foreman has all building science under his little finger.