Yeah, I had that trouble too, fireplaces are usually the first thing I build, so I can then create the room around it and sometimes I go overboard and use too many items >_<
Good rule to use is one item for the floor, one for the back, two for the sides, one for the top and one for the chimney. Of course if you build a more modern style fireplace you can get away with 1-2 items for the construction