Construction costs for new buildings in Cologne - basement?

Hello, what square meter prices should one currently expect when wanting to build new in Cologne? So really just the construction costs, a 560 sqm plot is available. I can imagine there is a huge range (from/to). It should have a medium standard. Two-family house with staircase up to the attic, so 2 full floors plus attic conversion. Size approx. 10 x 12m, I think that results in about 2 x 100 sqm apartments plus attic. According to the development plan, up to 12 x 12m is possible. We want to convert the attic ourselves, but it should be prepared. Water, electricity, etc. Preferably with an architect, meaning not a prefabricated house. Basement is welcome but probably too expensive, we would need a WU basement. But also your experiences regarding this are welcome, it’s roughly about the costs.

Only the construction without additional costs without garage without facilities in Cologne simple standard for a two-family house at least €2800 - €3200 per m2

With an external dimension of 10x12 m, you will never get two apartments of 100 m² each.