At what point is a boiler big enough to be steel instead of copper?

[gwrdriver]

A Reeves caution,
Some years ago I could buy excellently formed copper plates, delivered, from the "old" Reeves for about the cost of the raw copper sheet over here, but that's very much no longer the case. As most of you know, costs, prices, and shipping have skyrocketed.
The latest set of "new" Reeves plates I examined, furnished by a 3rd party, appeared to be formed by someone who had never built a boiler and didn't know what the shape of the end product needed to be in order to do its job. Particularly poorly formed was the throat sheet. Granted, it was a complex form, for a sloping firebox, but as-supplied it couldn't be used without considerable re-working.

[baggo]

Reeves have recently sold off all their boiler forming plates and their boiler 'kits' only have the flat sheet and tubes now so I presume they can no longer supply flanged plates.

John