Where does the construction cost calculation for financing come from

Good morning,
I am concerned about where the construction cost calculation for the real estate financing comes from?

We have a cost estimate according to DIN 276 from the architect. However, the architect is not involved in the construction execution. Does the bank now necessarily have to be presented with this cost estimate (signed by the architect?) and is the construction sum binding?
How does it work if I have already obtained quotes for some trades and these now differ from the architect's cost estimate or if I simply estimate the costs higher myself?
Or can I just submit a completely separate cost estimate to the bank (however I have calculated it)?

Thank you

Hello,
our financing is through Ing-Diba and we have submitted our own cost estimate with a fixed price offer from the construction company, the land price was also clear, but the costs for connections, earthworks, electrical work we partly estimated. There was no further inquiry from the bank. At the time, I also feared they would want it signed again by an architect
Best regards

Ditto - we have submitted a preliminary offer from the contractor and estimated all other costs. Better a few euros more than too little. We are probably doing quite well now (although - you shouldn't count your chickens before they hatch).

Also our contract for the turnkey house was accompanied by a rough estimate of additional costs such as internal development, access roads on the property, permits, etc. Since only price ranges were given, we had to manage on our own and check everything. On the one hand, other things came up, there were more and more items to specify and to correct repeatedly. For example, in our case, the personal contributions such as flooring and painting work were adjusted upward by me a dozen times until I felt comfortable with the calculation. The problem is: if you miscalculate, the bank will not necessarily notice. Surely they will inquire about the shell construction costing 10,000 € whether you forgot a zero. But if the architect has calculated a standard bathroom, yet you want mosaic tiles costing 180 €/sqm throughout the whole bathroom or a Jacuzzi tub, then you should also adjust this item upward. If the calculation lacks the garage but you want one, then this item may also be missing in the house construction financing. Therefore, it is even important, if you have concerns about an item, to correct it (upward). I would not reduce it downward, this buffer is quickly consumed by other things again.

Since I am not yet at the stage regarding obtaining quotes or architect calculations, I will simply ask my question quite casually. Would there not also be the case where, after obtaining quotes for all trades and positions such as electrical work, heating, windows, etc., one goes to the banks to consider the financing issue? Or would that now again be the desired ideal case?