There are times when my guys just won't go out to potty, specially when it's raining. They really don't like to get rained on for some reason. Other times, they are prevented from going out, so, they have to make do.
I have a Doggy Door in the Utility Room that is tiled. I put paper down in front of the DDoor, like when it rains, and let them decide if they want to use it, or, move on out to do it outside. Usually, they will (conditions being right) will elect to go on outside to potty.
But, when they use the paper, I do not scold them. Though at times I'm not sure why they elected to use the paper, I trust them, and I think they know that.