Somehow your questions, BeHaElJa, seem a bit confusing to me. Why?
1. If the building application has been submitted, the structural calculations and the thermal insulation certificate must probably already be included. So why is there still consideration now to intervene in these points and possibly have to redo or change the building application?
2. Do you really mean recessed spotlights (point lighting, accent lighting) or rather downlights (general downward-facing lamps)? The latter can certainly also be used for area lighting, and I personally would always do it that way again (namely a mix of downlights and regular light points). It is advisable, however, to plan exactly where these will go BEFOREHAND (i.e., before ordering the plaster ceilings) (and thus also how bright they are, what the beam angle looks like, etc.).
3. The price difference in material between standard (What is standard for you?) and engobed clay tiles will not help you much because they are possibly not only engobed but also have a different format, which means that the roofer has to batten differently, so the price for that may also change. Switching from concrete roof tiles to engobed roof tiles for a good 200 m² of roof area cost me about 3500 EUR, which I do not find too expensive for the added value offered (appearance, durability).
Best regards
K1300S