Hi Aggie
Sorry, not much good at DIY so not sure what you would cut the plastic with, but hopefully your neighbour will know.
Sizes of holes vary from CD size down to – one person had a door sized 10.5cm across and 9cm. high and apparently it was pretty successful at keeping cats out. It was though in a wooden box. Don’t forget to put tape (i.e. duck tape, or the like) around the entrance, so there are no sharp edges.
I have a feeling that it’s mostly hoglets that decide not to hibernate (those are the ones I have mostly heard about, anyway) but it will be interesting to hear whether those there do or not.
Good luck with the new feed box.
