Nigel,
Atom3D does have the Shell tool mentioned by Jason & Martin. It can hollow out a solid, and remove selected faces at the same time. Shell is almost certainly faster than either of the modelling approaches you have just outlined. Shell only requires one sketch for a simple case – either the internal or external profile. Having only one sketch, without any offsets, makes subsequent edits easier.
https://help.alibre.com/articles/#!alibre-help-v28/features-standard-features-shelling-creating-a-shell
The method chosen ultimately depends upon
- Which tools you are comfortable using
- The final purpose of the model
Sometimes you want to model the full details, reflecting how it is constructed – other times you might just want something that has the correct shape and need not include fine detail.