My lovely DIL volunteers with Hart Wildlife Rescue, specialising in hedgehogs and has become something of an expert. She fosters abandoned hedgies, as she calls them, feeds them up, cares for them and houses them until they can make their own way in the hedgehog world.
A couple of points which she has stressed to us is that it's important to keep an entrance and exit clear, but not so clear that cats, badgers etc can get in. Hedgies can fold their spines down and squeeze through the smallest spaces. Cat food and water in another dish are good, as is some shelter under leaves etc. Also, and I still am not entirely sure about this - they love hard-boiled eggs.
A bonus is that they get rid of those horrible, slimy plant-munching monsters. (I have a phobia - makes my fingers tingle to even type their name, so I won't, but you know what I mean.)
Good luck and according to Zoe, the DIL, you've gained a low-maintenance pet for free! As well as being a bit of an expert, she's also slightly obsessed, but we love her!! 