Wall are covered with these panels http://ceiling2floor.co.uk/product/pvc-1000mm-widepanel-light-grey-marble/ and very nice they are too!
10mm thick plastic, looks very similar to corrugated cardboard from the side.
Problem is that there is no way to fix a shelf to the glass enclosure, so it will have to be attached to the walls somehow.
Considering that it will need to hold around 5-6 full 0.5l bottles of shampoo/conditioner/shower gel/etc, possibly more (don't ask...), would any of the suction-type fixing be up for the job?
Otherwise, how would the panel suggest fixing it to the wall panels (plasterboard behind)? Simple masonry rollplugs?