What do you think? -- can I do this?

I'm thinking of getting my gerbil a new cage, one with multiple levels (a lower one, so he doesn't fall and get hurt). I have a small area in my backyard fenced off with wire screens for the gerbil to run around in (we don't use pesticides). He always loves it when he gets to go out. So, I was thinking of putting some potting soil in the bottom level and sprinkling some gr seeds over it to grow gr (I'd still bring him outside, though). I also want to try sand (natural habitat) (maybe that should be at the bottom instead) and the rest would be covered in the aditional aspen. The aspen and sand would be replaced weekly, and I'd just sweep any visible...deposits (xD) out of the gr and water it when I clean out his cage once a week. So, do you guys think this would work?