The width of the shell depends on the “last” the manufacturer uses to form it. Different models or product lines use different lasts.
For example:
The Tecnica Diablo fits a men’s B to C foot width. The Tecnica Vento fits a D to E width. The Tecnica Modo goes even wider, and the Tecnica Vento HVL (HV stands for High Volume) is probably the widest boot available.

For women’s boots: I’m not sure of the exact specs but I have very wide feet and I find that Saloman boots fit quite wide. I’ve always used them.