I'll roughly say Siegerland. Which providers have you talked to so far and what budget do you mention when you go into such a conversation?
I thought Siegerland is NRW. But you specified RP as the construction site.
Our current favorite is Keitel-Haus. The disadvantage I see: they are very far away (locally). In addition, a regional timber frame builder who also offers turnkey construction (an absolute must for us, since we are over 500 km away from the construction site). I will not mention any budget to the providers at the beginning: of course, they ask for it. We have compiled our requirements (which rooms, which area, which features, how garage/carport, where floor-to-ceiling windows, etc.). Plus the house style and desired extras. And I go to all with exactly the same documents. Therefore, the starting point for the first quote is identical everywhere.
That makes analyzing the quotes easier—but it is still difficult enough: they will never be exactly the same. Also, providers deliberately do not include certain things in the first quote (at least that’s my perception). You have to be persistent then.
We want to have three quotes—and then go into the next round with two of them (meaning preliminary sampling, more detailed questions/agreements; scheduling, etc.).
At the same time, of course, list all "additional costs" (especially ancillary construction costs): these differ enormously. At the beginning, they are certainly not complete—but then insert placeholders. Others clarify either with the provider’s quote or through further inquiries (such as connection costs).
Our goal is to have a fairly precise cost breakdown before deciding on the provider—and that with all costs included.