For the extension, I have 1250x1750mm window openings in 24 brick casing. The openings are flush with the ceiling, so no additional lintel is needed. Now I want to install windows, but no louvers, but I want to hang the ceiling from the inside, maybe extensions from the top so the turn-and-tilt is not possible to the ceiling. The possibility of extending the frame at the top (100 mm).
However, how do I plaster this on the outside so that there is an even opening on the sides? Can I use drywall for the interior finish?
I don't see any concerns here about the inability to apply plaster cleanly and evenly. Doubling is usually done with window profiles, so the frame just gets stronger or higher.
You can get by without doubling if a piece of panel is inserted on top. Assuming 250mm here, that leaves a 1250x1500mm gap as the "window". This also gives a lot of leeway in terms of suspension height.
Another option is to split the window as above, but install tinted glass.