I made one for my guys.
I used a crate tray, 2x4 and bought some high grade grass. It's poly and really mimics real grass, but holds no odor and does not absorb liquids.
I use washable pee pads underneath. I wash it even in winter and just put it back while damp.
The boys use it when we aren't home. Remy even poops on it.
Milo not so much.
EDIT: I made my own because it's twice as big and cost me less than half.