feed hopper on mouse rack

[Mark]

I'm looking into making a mouse rack in the near future and I'm really confused about the food hopper. I want to use the ones that are flat but I'm not sure on what size of metal wire or hardware cloth to use. How big do the holes have to be so the mice can get the food without the food falling through. Can anyone explain this to me. I have heard that low quality dog food is ok to feed the rodents. Is this true?

Thanks