So many questions…
Were there any contracts drawn up prior to placing the order?
If so then they can’t walk away s as they’re in breach of contract, the mistake is theirs, whether it came as a result of the steel fabricator, window manufacturer or anyone else.
Both the Arch and Eng drawings show the design intent and I assume these are to scale or dimensioned.
The contractor simply hasn’t built to the drawings. It’s an expensive mistake to rectify but that’s their tough ****.
So who is employing the architect, you or them?
Also, is the contractor a Main Contractor employing subs or are is it a builder carrying out all the works themselves.
It’s terrible that this is even happening to you but you shouldn’t be footing any additional costs. They were employed to build to a set of drawings and an outline spec and they’ve failed to do this.
How big a company are they, is it possible that they’ll pull the plug on their Limited company if you take them to court to avoid paying to rectify this?