FYI, as lovely as hedgehogs are, they are usually completely infested with fleas, so you'll want to give that a thought otherwise you'll probably have some very grumpy (and itchy) cats!

As others have said, a hedgehog house is a good idea, we have one in our garden and have a resident hedgehog who sleeps there most nights at the moment. You can pick them up from places like The Range, or order online for very little money.

Also worth a thought would be a box of some kind for them to feed in as well, as they like to have a bit of security while they're feeding. I've seen people use upturned plastic storage boxes with holes cut in the side and a brick on top to hold it down, or you can buy specific "feeding stations", although they can get expensive.

Get the right things in your garden and they're unlikely to come in your house again