Calculating land costs - who understands that?

The only comparable property (also on ImmoScout24) has 2000sqm, various special features such as a pool, sauna, granny flat, and lake view, and a continuously renovated house for 1,595,000,-.
With "ours," as mentioned, nothing was ever done. It was heated with an electric underfloor heating system (defective), the roof is leaking, and the rest is in the original condition, and the garden is very overgrown ☺️.
The existing granny flat has been empty for 10 years and is moldy.
The standard land value or market value is certainly over 500,- EUR.
Could you explain to me the number of full floors II= I+S?
We are still struggling a bit with the demolition costs, but we should assume some kind of value and start the price negotiation accordingly.

I unfortunately do not know how to assess the area. For us, it does not matter whether demolition is necessary or not. Therefore, there is no "demolition bonus". The same land prices are applied. Therefore, I would just make an educated guess for you, assuming all of the 975 m² is also building land, that a price between €536,250 and €585,000 is "realistic".

Theoretically, one could/must account for the demolition costs. In reality, it is more like it doesn't matter or that undeveloped land would be worth significantly more. Costs at the lake increase extremely. Since it is partly no longer allowed to build holiday apartments, prices are going through the roof. I have a case in my circle of friends. A new residential area with apartment buildings was developed about 4 years ago. The few remaining lots are now going for 40% above the original price. So about €10,000 per m2 developed.

Could you explain to me the number of full floors II= I+S?

You have a site cover ratio of 0.4 and a floor area ratio of 0.5
I + S
I stands for a full floor,
S probably stands for a gable or setback floor, at least it fits with DN and floor area ratio: above you are only allowed to have 1/4 of the ground floor with real ceiling height. Approximately.

A very layperson's question: how can I tell if everything is building land? The price is quite something, and it won't work with the new construction for under a million.

A very layman's question: how can I tell if everything is building land? The price is quite something, and it won't work with the new building for under a million.

This is a building plot for which a development plan exists.

But have a look at the legend of the development plan to see what the two dots mean. Maybe it indicates garden land ;)