"A tall policeman is standing outside."
Translation:Egy magas rendőr áll kint.
Both are correct. I would say "Egy magas rendőr áll kint" is the normal, neutral statement. If you say "... kint áll", that will direct some attention to "kint áll". Maybe the context would make it clear what exactly you want to emphasize. But if you really want to stress the "outside", bring it forward. You can even put it in the front:
"Kint áll egy magas rendőr."
You can also say: "Áll kint egy magas rendőr".