Hello. I use very large litterboxes for my servals. They are about the size of a large storage container, but the height is cut down a few inches. Something a little smaller than that would probably work for your dog to use. There are companies who sell various sizes of litter boxes for dogs.
As for litter, you can use newpaper that is shredded, wee-wee pads that puppies use (especially to start off with if your dog is still a puppy) or dog/cat litter that clumps, but, dogs do not bury their waste the same way cats do, so you have to keep that in mind. If you use the cat litter, keep an eye out to make sure your dog isn't ingesting it. If it starts to, I'd just switch to a different filler. Good luck!
-Calyx