Hi!
So, are you saying that you would write it this way: "What happens if we get the horse inside the barn?" That is a good way to write that if what you are asking in the story is about the reaction of the horse once it is in the barn, or if you are wondering about the condition of the barn once the horse goes inside.
However, if you just want that darn horse in the barn but you aren't wondering what will happen later, then it might be best to just say, " Let's put the horse in the barn now." or "I'm putting the horse in the barn, so you need to feed it!" Hahahaha!
It really is all about your character's motivation or intent.