Just about to ask the same thing. All I can muster from a quick Google is that the stadium has a decent car park for away fans but I'd rather not park at the ground.
There's a fairly big car park right near the gym next to the ground. Think it was a fiver, maybe a little bit more
Went in the away car park near the ground two years ago. It was a dream, straight in and out, cheap enough, easy access to the ground etc. Only been on the train other than that time so no idea where else to park. The car park is huge from memory so you're unlikely to get blocked in or anything.
Have a look on googlemaps, head for Miry Lane. We parked there when Dale played at the DW recently and it was decent for a quick getaway after too. Nice long road so plenty of options, the walk too and from the ground involves crossing a canal bridge. Simple enough and free.