Renovating an old building, are construction costs / effort worthwhile?

That may be. With us, it is completely normal and natural to help each other within the circle of friends. Last year, we redid a terrace at a friend's place and built a small pool + 60sqm terrace at another's. Currently, we are helping someone who bought an old house from 1910. We have already removed several tons of construction debris there. If someone had shown up to give me money for the help, they would have gotten a few gentle pats on the back of the head. Of course, it always depends on the extent, but as a friend/buddy, you generally never accept money as long as it's within the usual scope.

It is the same with us, but no one would come up with the idea to renovate an entire dilapidated house in this way. It is one thing to dig out a terrace together over a weekend and wrap it up with a barbecue evening and a few cases of drinks, and quite another to run a 12-month construction site.

Why is the house being sold? Did the sellers live in it themselves?

When you say that the roof and the windows were just newly done. That sounds to me like the seller started renovating and then realized that it’s more effort than expected or too expensive. And now wants to get rid of it again, preferably without a financial loss.

I would definitely have the house looked at by a professional who can say what absolutely needs to be done. Since your budget is limited and already quite tight, you should check that carefully before buying. Otherwise, a house like this can financially ruin you. And whether it will be that easy to sell again is another question. Are there many interested parties for the house?

It may be. With us, it is completely normal and natural to help each other within the circle of friends.

I congratulate you on having "real" friends - often, in such hopeful speculations here, acquaintances are rather meant by "friends," and a deficit of reciprocity in opportunities for help is unfortunately widespread nowadays.

But I don't think the OP will comment on it anymore. ;)

You always assume from your own perspective. And with us, it has also been the case that for about 10 years, since the first person bought a house, help has been given all around. Over the years, 2 renovations, 2 new constructions, and one refurbishment. Of course, I then assume that the friends are just as helpful. Under no circumstances would this be a weekend project. But especially chiseling work can really be done well by yourself. This saves a lot on external labor time. Also, gluing drywall, leveling floors, and similar tasks can be really well managed with a bit of ambition.

Our helpers are of course compensated, but no one expects it. Because 95% of the helpers belong to the family, and with us, everyone helps everyone. A bricklayer and a carpenter were also present during the inspection. And we will also help as much as we can. If someone explains it to me properly, I will insulate the place too, but I will not stand there with an open YouTube video and hope it’s right. We have the opportunity to renovate it with professionals, and then I would also like to have one of them by my side. Since the house is not yet online and we only came across it because another purchase fell through, I don’t know if there are other interested parties. The house is being sold by the heirs; until two months ago, the parents still lived there. The floors are slightly uneven, measured in millimeters, not centimeters, we just don’t want floorboards. Likewise, the ceiling is purely a matter of aesthetics and not 100% straight, like the floor. But once you’re inside, why not? I will support everyone and not leave family and friends to handle it alone. There is also more than enough that I can do without a professional, and I will do that. If I ever have a question, I can call anyone at any time. The bricklayer looked at the walls, so we know they are a bit damp and not soaking wet; if I chose my words poorly before, I apologize for that.