List of incidental construction costs. More expensive "on the builder's side"?

So after some conversations, most people declare me crazy for 15%, but it is probably a realistic average value based on what I often read here!?

I am regularly amazed at how quickly even larger buffers are used up. So I would rather calculate 15 than 10.

I assumed 15% incidental construction costs + costs for earthworks, but I think that might be too much and one can also exaggerate. Yes, when it comes to earthworks there are basically no limits upwards, but there should be a limit in the calculation somewhere, otherwise there will never be an end. I think 15% without a separate extra item for earthworks should be within the range...

So better with a buffer, but actually we are calculating 10% of 400k as additional construction costs including the earthworks.

We have planned:
10k house connections public utilities
20k earthworks
10k miscellaneous
(5k buffer)

House connections plus earthworks just barely stayed within budget and almost none of the other 10k has been touched yet.
I wouldn't know what should come in dimensions of 10% of the house price????

I looked up our values from 2019 (rounded):

Building permit 800,-
Excavation work 18,500,-
Sewer connection with inspection chamber 7,000,-
Structural engineering inspection Hessen 1,600,-
Construction electricity, construction water, waste disposal, etc. 2,000,-
House connections for water, electricity, telephone 6,000,-
Laying ring earth electrode 1,000,-
Measuring ring earth electrode 350,-
Road closure 350,-
Final survey cadastral office 1,000,-
Professional association 200,-
Ordering and registering land charge 1,000,-

This corresponded in 2019 to around 13% of the house and land price for us.
Anyone calculating with 15% in 2021 would do well.

Thank you, as I said, I will keep the 15% and will never be certain but will drive very realistically with it. Because especially the groundwork + excavation, which are usually the reason why the budget is exceeded, are already settled. Excavation goes to acquaintances, unless we even need everything ourselves, and the excavation work is more or less already safe.