Buying a shell construction - What are the costs and what else should be considered?

What should be considered when buying a shell construction from a private seller? And what is something like that worth?

Known data to me: Floor area 9 x 11 m; exterior walls unfilled bricks 36.5 cm thick (including basement); basement-ground floor-upper floor-attic; flat roof; concrete (precast) stairs, windows are also installed

Missing: ETICS (20 cm planned), wall plaster (outside and inside), tiles, floor coverings, screed, underfloor heating, ventilation, etc.

I see the condition as a non-expert as so-so, since apparently in the evenings some tinkering was done from time to time: a few meters of cables laid and a few sockets drilled into the wall. Also, a few pipes were sunk in the bathrooms. The masonry... in some places you can see into the interior from outside because there is 3 cm of air between two bricks, which was only attempted to be closed with a bit of mortar, etc. At some windows, hand-width fragments were placed underneath because there are no window sills.

Since the bricks of the exterior walls were drilled or channeled (for cables and pipes), I assume that this must be accepted due to thermal insulation? Because if you fill these holes with putty and create new channels and sockets a meter next to them, you have increasingly destroyed the insulating effect of the cavities in more and more places?

Comparable houses of similar size from solid house builders are turnkey at around €240,000 to €300,000. Would such a base even be worthwhile? And what would such a base even be worth?

Nothing if you ask me, and a box of trouble comes free with it. Can it still be tracked which cables were laid how? And electrical partly already installed? Risky business, I would say. I'll put it this way, someone who botches the masonry like that was surely especially careful with the foundation...