How about without the "egy"?
I wrote: "A magas épület egy kórház van", is it wrong or correct?
Wrong, when you describe something, you don't need to use "van" but hey, at least you put it in the correct place because that's where it would be if we used "van" in third person singular. :D
Duo, when one (now) hits "complete", Duo is GREATLY diminishing the coloration of the reply. PLEASE LEAVE IT as normal, ie, coloration of the letters/words highly visible.