Pressure-treated wood is great at standing up to moisture and rot because it’s impregnated with arsenic and heavy metals. However, these are poisonous to pets and people. For this reason, don’t use it for the floor, walls or any other parts of a doghouse that will come into contact with your pet.
That said, I used pressure-treated wood for the base frame of Chase’s saltbox because his house will sit on the earth. The siding overlap minimizes the amount of pressure-treated wood that’s exposed, but I’m keeping an eye on him to make sure he doesn’t chew it. If he does, I’ll cover the exposed frame with plywood scraps left over from making the house.
By the way, I was careful to wear work gloves and a dust mask when I was working with the pressure-treated wood. You should, too.