My normal storage is map cabinets, steel by preference (no problems
with shell-damaging acids being released by oak or particleboard).
With thin plastic foam (preferably museum-grade) lining inserted to
stop trays sliding around, the drawers are just great for storage of
the vast majority of specimens. Of course, without foam in place you
could get slightly larger specimens in, but they'd slide every time
you opened or shut a drawer.

The roller-type drawers are best, as they don't produce a dust of
rust and paint to drop into the shells along the sides; however they
mean the drawers are slightly narrower and they CAN come loose, so
there is some risk that the drawers can derail and fall out while
open (believe me, it can happen... and has, though in my case they
tangle with the rails and so don't actually fall or tip much). These
are also a LOT easier to open, especially if full of relatively heavy
fossils full of matrix.

Personally, as my collection is a scientific one, I'm not into
displaying, beautiful though these can be. The only shells I have in
a glass-fronted case are those too big (Spondylus, Perotrochus,
Strombus leidyi, Tonna, Argobuccinum, Pleuroploca, Busycon, Volema,
Vasum, Turbinella, Nautilus, Allonautilus and blocks containing
fossils) to fit in my normal cabinets.