Super, have you considered these type of cases? They are intended for Lego models/figures, but they do have 3 tiers as standard and of course being Lego you can make the rear platforms higher/wider/deeper to suit using Lego bricks if you want. If you go to a Lego store you can usually pick up the flat tiles as well (i.e. no pins on top) so you can end up with 3 tiers with smooth surfaces in whatever colour you want if you're lucky
Here's a link to one on Amazon UK; https://www.amazon.co.uk/XIN%C2%B7SHI-Mi...WNrPXRydWU=
Here's a link to one on Amazon UK; https://www.amazon.co.uk/XIN%C2%B7SHI-Mi...WNrPXRydWU=
Happily collecting things all my life...