We live in an apartment building, and the landlord doesn't allow us to use the side of the building (only patch of grass nearby, unless we go all the way to the park!) so have our balcony.
My husband saw this and built one himself with astroturf!
He made a little box with a couple of pieces of wood, and a few layers of the turf. We clean the top layer and rotate the layers every week or so. That way we still have our balcony, and it's more like a (dare we say) litter box.
It was so much cheaper, and it's trained Derby to use grass and not pee pads
We did use pee pads in the very early stages because he couldn't hold himself all night, but that was only for about a month, and now he can hold himself all night! He barks to go outside now, so we're all good!!
It's fantastic.
We know it's time to change the astroturf (like when it's been awhile and maybe we've forgotten when the last time we rotated lol) when he started to do his business on the balcony.. lol