Have raised slate tiled floor, need recessed cover say 200mm x 200mm into
which I can put a piece of slate tile so cover is unobtrusive. Where can I
get one? What are they called? Build Center et al websites are grade A
pants. Is needed for access to drain cocks for central heating which then
drain away through pipe under new floor.

Plus any tips for grouting uneven surfaced slate with mortar mix (this is a
semicovered mini-courtyard)?