Demolition and rebuilding or renovation? Which house?

I probably need a power of attorney from my father (owner of everything)?

I don't know the customs in Bavaria. In NRW, no power of attorney would be necessary for construction consultation. Here, theoretically, you could submit a building application for the neighbor's property without them knowing anything about it.

However, I thought the foundations are still "good".

Since you have admittedly no idea about house construction, you can consult an architect or another building consultant of your trust after the construction consultation. In my experience, a core renovation rarely pays off.

I asked if I should wait because currently companies are overloaded due to the construction boom in Germany?

I think it is a question of contract design. Without deadline agreements and descriptions of the consequences of non-compliance, it could of course turn into a never-ending story. Whether the situation will change in the near or distant future, no one can say.

I have the feeling that you see building an apartment as relatively easy, clever, and business-savvy.

That is probably currently a flea in some ears, that there is a good start-up climate for people who want to grow the “fruit” of living space almost as part-time farmers. However, being an investor is still only worthwhile for people with a certain surplus of wealth or creditworthiness.

I don’t know how high this funding is, but basically it applies that you don’t get anything from the state for free without conditions or investments.

This is probably more specifically about such subsidies that are granted for securing rural settlement density. However,

50 km from Munich is a normal commute for many there...

sounds more like the place is within the catchment area of metropolitan land seekers. Where the market has enough pull, such subsidies are not praised.

Neither of the two buildings are “lovely gems.”

Then they also don’t open romantic city dwellers’ hearts.

However, I thought the foundations were still “good.”

Naively considered, exterior walls seem, due to their considerable contribution to the volumetric appearance of the building, as if they were “almost half the house,” in other words: as if you could already leverage this asset.

But first, even “new” they only make up a fraction of the shell construction costs, and secondly, the walls (apart from the installation of openings) would first have to be brought up to a contemporary standard. Starting from a single-layer solid brick wall probably 38 cm thick is a long way. Better consider the walls not as an economic good but only as a recyclable material.

I probably need a power of attorney from my father (owner of everything)?

I would not carry out the generational transfer of the real estate assets according to the development of the properties; otherwise, you merely burden the improvement with later inheritance taxes.

Thank you for the many answers, even if some were somewhat sobering ;-)

I take away that in both cases a new build is probably better and the "good" foundations (and the uninsulated roof) don't help.

Also, only the site of Grandma's house is guaranteed to be buildable, the district office will give me information about the hay barn (larger ground area with adjoining garden) (I'm rather pessimistic).

By the way, I don't want to do big business, but only not let unused buildings and capital lie fallow. At some point, after the tenants, maybe our son (currently a toddler) will move into the house, but one can't really plan that far into the future...

Furthermore, only the plot of the grandma's house is guaranteed to be buildable,

How do you come to that conclusion? - in view of

It is located on the street and practically has no garden.

I put a big question mark behind it.

[...] convert for rent (to rich Munich residents ;-) according to new standards? [...]

There is somehow a flaw in the logic. Rich Munich residents would be damned if they lived 50 km away from their city and employer. :D

There is somehow a flaw in reasoning. Rich people from Munich will never live 50km away from their city and their employer. :D

I think that Thomas 1112 was thinking of a second residence for "rich people from Munich" or retirees who don’t have to commute daily. For me, a second residence would have to be by a lake. Maybe he will enlighten us.