It was clear to see that the OP had slipped into sarcasm.
I had also already finished construction (shell construction completed). For the bank, I then made a list, on which the remaining trades needed were listed, along with the sums it was expected to cost. I could support part of it with concrete offers, which I then included; for others, there were estimated values (each provided by a specific company, which was also named - so it could have been verified).
This was accepted as it apparently seemed plausible enough. No one wanted a signature from an architect or similar.
So your bank wouldn’t accept it if you submitted the floor slab with a separate offer? That’s strange.