Old building apartment - retrofit gas heating, house without central heating

Hello and thank you very much for the quick responses.

The exterior walls are partly 40 cm, partly thinner - but I believe none are under 30 cm and they are solid, all in all a very solid building structure. I think the static structure should actually be taken into account - this is the top floor, partly already the sloping roof and above that the unfinished attic - there is no underfloor heating, the floor covering is currently still linoleum - regarding the orientation of the building, it should be mentioned that it is nicely aligned - many rooms with south or southwest orientation. I cannot say the exact ceiling height, but just from the entrance door I would guess the typical old building room height - but I will measure it.

The windows are already fitted with insulated glazing, the apartment was renovated in 2000, the roof in 2003 - what exactly was renovated or insulated back then I will of course have handed over to me and check.

Regards

I will simply schedule a viewing appointment for next week and convince myself on site - I cannot say for sure about the floor of the storage room, however the roof rafters are exposed - as it looks, the roof structure currently has no insulation at all. But let's wait and see, drink tea, and visit. Since I plan to occupy the whole thing as a shared apartment anyway, the additional costs would be divided by 4 and, if the roof structure is converted, by 5 or 6.