I think this should be easy for our wonderful dev/designers to whip up in meer moments.
I have been thinking for some time that I would love to build in grated flooring.
All that would be needed is to add…
Arena grated wedge
Arena grated ceiling tiles.
Built over the open air to see the room below or built over water or lava would make an impressive view.
There are currently two ways to accomplish that. One is to use flotsam ceilings:
Blends in really nicely with certain wooden building pieces.
However, if you don’t have Siptah or you’re not building wooden floors, the other good alternative would be to use a hatch frame in whatever style you’re using for your floors and then put a reinforced hatch door (variant A) in it:
This one can blend into any other building style and it doesn’t require any DLCs.
I hope this helps 
Be cautious using these Reinforced Hatches as walkways as followers will
They look great, and can support planters. Just be advised if you’re building “sparely” for PvP, you will cry a little when your fighters are all stuck in hatches because someone tried to creep up on your castle.
I’ve thought of the hatch door but moving around especially while sparing or maybe just regular in game life one might open those hatches easily and fall through.
Plus if it’s a room built into a octagon shape using wedges and squares the wedge would be missing.
I envision that the metal grates would look better with the other t3 building pieces since they will look like the grated metal doors.
I love the flotsam building pieces if I’m building a beach house of sorts.
No offense to the devs, but I hate the pathfinding in this game so much 
It could use some love