Extension/Residential Expansion (NRW) /Shell Construction Costs

I come from the Dortmund area, we have a small old miners' house. I would like to extend this house. I wanted to ask you here in the forum what approximate costs I might expect. Extension 2 floors without basement. I am allowed to build an extension and I also know which distances I have to keep, because I have already asked the building authority. And in my settlement, many similar extensions already exist. Additional construction costs: With an extension on an existing developed plot, there are actually no major additional construction costs, right? I do not want to hire a construction company to do the entire extension for me. We have bricklayers in the settlement. Only for the foundation slab and floor slab and roof truss do I want to hire someone. My calculation: Shell construction costs: In the attachment you can see a picture of how the extension is supposed to look approximately and a simple sketch of how my extension should be. Approximately 7 meters long, 8 meters wide, after about 3 meters it gets narrower, about 6 meters. I have an architect who offered me a fixed price including statics for 3000€. Approximately 130 m2 masonry 1m2 stones about 22€ = 2800€ Foundation slab: about 5000€ about 50m2. I asked a small company, the man said he could do it for 5000€. Is that realistic? Floor slab: The floor slab should be constructed from filigree slabs. 1m2 about 22€ So the slabs about 1100€, then + crane + workers + concrete + reinforcement, so about 5000€ as well, realistic? Masonry work: As I said, I know enough bricklayers but they want some money too. Masonry work per floor about 3 days, right? That is realistic, isn't it? 2 workers 15€/hour about 720€ per floor (masonry work costs) So about 1500€ costs for bricklayers Windows/doors: about 6000€ Roof truss: Well, I have absolutely no idea what the roof truss would cost approximately. You can see in the attachment the roof of the reference extension. What does such a roof truss cost approximately? Will 7000€ be enough? Summary: Architect: 3000€ Foundation slab and floor slab: 10000€ Stones: 3000€ Workers masonry work: 1500€ Windows/doors: 6000€ Roof truss: 7000€ Miscellaneous: 2000€ ------------------------------------------------- 325 00€ shell construction Is that realistic? And have I forgotten something? Many thanks for the help. Best regards

Unfortunately, I don't have any numbers for you either, but have you already started and can you tell me your costs?