I see. I definitely did not get your question
- you can import the conventional bulk structure (cubic) and repeat the structure nxnxn times.
Just enough to form a single repetition unit of your grid, not the whole structure.
- Select the atoms to delete by using the Select>By Expression tool and write something like "z>5 and z<15 and y>5 and y<15" to have channels perpendicular to the yz plane for example.
Also selecting the atoms with the mouse works well.
- delete those atoms.
- repeat the structure to form your grid.
about the interfacing, you should create an oxide slab with similar dimensions of your metal grid in the xy plane and then you can use the interface plugin.
if you do not need to adapt the two cells but only "deposit" the grid on an oxide layer then you can create an oxide layer which is bigger (in the xy plane) then the metal grid and simply drag and drop the metal grid from the Stash to the oxide layer configuration. Then translate it wherever you wish.