As you want a suffix as well as a prefix, you will need to edit the
ShowRoomDescription function. Just be aware that if the function gets modified in a later update to Quest, you could have problems, so it has a slight risk. Do show library elements and find the function, then copy it to your game. Go to code view, and look for this line:
objects = FormatObjectList(game.pov.parent.objectslistprefix, GetNonTransparentParent(game.pov.parent), Template("And"), ".")
And change it to:
objects = FormatObjectList("There's ", GetNonTransparentParent(game.pov.parent), Template("And"), " here.")
With regards to adding "a" and "an", Quest does that automatically (you can override it for a specific object by unticking
Use default prefix and suffix).