TSK is just ridiculously expensive.... Michendorf? But even there the building land costs 200€ per square meter
On the other hand: It's in the commuter belt. No matter how much debt you take on. In 10 years the place will be worth at least twice as much, the parameters shift accordingly with the follow-up financing. And even if not, as soon as the house is finished, you can come out of it with a profit. With similar conditions (80k equity) we would build a house here for 3/4 million... a relaxed 2000€ installment... In 10 years you pay the same for your rental house, and after 12 years my rate is less than a comparable rent...
I don’t see it quite as radically as you do, but I also assume further appreciation of the land alone. The foreseeable rising rent is also a reason for the building project. Nevertheless, primarily it should be owner-occupied living space.
Would it be an option to buy a plot a bit further out that costs 120k to a maximum of 150k?
How big is the plot anyway? Could it be a bit smaller?
Up to my pain threshold regarding distance, it is now 250 EUR/sqm. Smaller plots are not available for the reasons mentioned.
How big is the plot? Maybe there’s still the possibility to split it? Semi-detached house on the plot?
Splitting is unfortunately hardly ever possible. A semi-detached house as a "last resort" is already being discussed, but only if it is truly unavoidable.
Just something to think about. For a loan amount of 450k€ over 25 years fixed interest and 2% repayment at current conditions and 100% financing considering your building location. It’s anything but nice!

Which calculator can you recommend? It certainly isn’t nice, hence this topic
Hello,
we took out a loan of 400k last year, pay 1,400 euros per month and are theoretically done in 30 years. Due to your low equity the conditions are different for you: First, you won’t get "our" 1.55% because of the higher loan-to-value ratio, and second, the overall project will not be manageable with your budget. The missing floors, kitchen, painting, and landscaping are not done for free.
If I were you, I would get offers around ~450k with 10 years duration. Only poor people and those who can’t calculate take 25 years. Maybe you’re lucky and get an affordable offer from your bank. If not, you’ll have to save more or look for a "cheap" plot.
What equity would be needed for significantly better conditions? The problem at the moment is that land prices are rising faster than you can save the money. There was 10-20% growth per year in the surrounding area in the last 10 years, no end in sight.