I cant seem to find metal grating..ive looked at home depot and lowes. Any advice on where to look.?

On the lofts with grating on the floors, how do you clean under that? Surely the poop & debris must accumulate where it needs mucked out? I have my breeding loft of 6 X 8 with wood floor that I sweep & clean up daily, but need to build another loft strictly for fliers, something low...