hi..the trays are for like rabbit hutches..etc...i got them at Tractor Supply store..(they have all differant sizes)..i think most farm/feed stores will have them........but i bet you could use anything ..old baking pans.,cookie sheet..
..i even had a boot tray under there at first..then my hubby just nailed a board across the back wall of the coop...and another board further forward(he measured the withe of the trays)....then we just set the trays on the 2 boards.....and then he put the roosts over the trays(just nailed 2x4's to the support beams of the coop walls) about 18in from the wall or so....used our old parrot ladder for them to get up there with..and...
..so far its working..it really does keep the coop cleaner...having a drop board..
thanks - went to Tractor Supply but hated their prices: $14.99 each!!! so i went to Lowes and bought some black rubber cement mixing trays for $5 each. deeper than your trays but my pockets are also a little deeper now... thanks again!