I’d advise not to treat it with anything, and yes it will eventually rot down and you’d need to make a new one, but I feel that will be a lot better for a hedgehogs health.
I have a hedgehog house but not treated with anything, I just put plastic sheeting over the top, and then brash, twigs and leaves, on top of that.
A lot of hedgehog homes that are for sale have roof felting on top, and the roof has a bit of a lip to protect the house from rain.
Best to use untreated wood, and not risk the hedgehogs suffering from toxic fumes.
