Old building renovation (1966): Two-family house - floor plan sketch

First, the pipes etc. and the roof will be renovated. The windows are not from 1966 but from 1998.

Windows from 1998 already have thermal insulation glazing and a Uw value around 1.5 W/m²K – I would also leave them in if the fittings are still in good condition. Possibly renew the sash seals. I would rather see if I can get a few more windows on the south side. As the house is positioned there, the living area, especially in the afternoon, will be very dark.

You are now planning 200k€ for new electrical, water/sewage, roof, and some walls/masonry work as own labor? I wouldn’t even know where to spend that much money on materials.

Ok, now I get it. So it's more of a rooftop terrace. I really think the parents' area is way better now! I would still consider, even if the bathroom is relatively new, whether I wouldn't incorporate the narrow toilet into the children's bathroom. If that was only 4 years ago, maybe you can still get the same tiles and don't have to redo everything? A short wall at the bathtub can remain as a privacy screen for the toilet. The door to the bathroom can be bricked up and only the toilet door kept, then it would be a nice bathroom. Now there are only two narrow rooms. I once lived in such an old house and the toilet/bathroom solution was similar. That always annoyed me because you had two rooms where you simply felt cramped. However, I was renting then (and wouldn't have invested in a renovation) and secondly, the bathtub was against the wall between the two narrow rooms, so it wouldn't have been as easy as here. But at that time it was probably "la dernier cri" to do it that way.