Construction ancillary costs not visible?

Hello everyone,
we are in the process of building a house.
Before signing, it was stated that the ancillary construction costs would amount to approximately €50,000.
Now, he told me, two months after we signed (construction has not yet started), that it will probably settle around €60,000.
There are a total of 2 semi-detached houses as well as a single-family house. Behind that, a multi-family house will be built, which will not be sold but will remain the property of the developer.
He said it is not normal for the builder to look at ancillary construction costs, such as electricity, but that the developer determines how high everything will be.
For example, Kabel Deutschland will also be installed. I do not want this because I want to save the costs since I will install a satellite dish. It was said that Kabel Deutschland will install it for me free of charge because the rear multi-family house will be connected anyway. Of course, I can now trust that I will get Kabel Deutschland for free. He will not show me an offer from Kabel Deutschland, because, as already mentioned, it is not normal for the developer to present the invoices to the builder.
Can I accept it this way? Is this correct?

Thank you very much
Wangry

Are you building with a property developer or with a GÜ / GU / BU? If it is a property developer, it is usually the case that you have a contract for one house (one unit) – you should not incur any additional costs; for everything else, it depends on the contract – often everything from earthworks, to house connections, to the outdoor facilities.

Alternatively: what exactly does your contract say about additional construction costs? Feel free to anonymize and upload.

No idea what to call it. He calls himself a construction supervisor. The contract states plus ancillary construction costs. This accordingly concerns everything. Demolition, laying cables, construction power, etc. The construction supervisor manages everything for me, including, among other things, as mentioned, the Kabel Deutschland matter. But invoices or offers are not submitted to me. Even looking for a demolition company myself makes no sense, since, as mentioned, several houses will be built on the property. However, I must say this is currently common practice in Hamburg. Unfortunately, you can't really choose much in the current situation.

Strange construct and not even clear if it is permissible. He sends you invoices for the services rendered from the category [Nebenkosten], without explaining their composition or stating their amount in advance? Sounds a bit like you gave him a blank check...

Well, I didn’t sign anything with him. He only asked what it would all cost. At the latest, I will be able to have insight in court. However, the construction management company has been on the market for decades, and if you read online, you only find good things about them. But what do you think about the additional costs of around €60,000 for a 350m² plot, a 100m² house, and a full basement? The additional costs include everything except for lawn, fence, carport, and garden shed. Everything else is covered.

It must be said that he can’t know in advance what the soil condition is like and therefore doesn’t know how much soil needs to be removed or added. He also can’t know about construction electricity. Apart from an estimate, he can’t provide anything else, or am I wrong?

Of course, you can't know that – but in any normal architect-client relationship, you get to see invoices and receipts. €60k without knowing the service – concrete paving for €10 per sqm or natural stone for €60? Ground conditions with pile foundations or is there topsoil over non-cohesive sand? I rather suspect that the fee for site management is also included – then €60k is acceptable if everything is properly planned and supervised.