Upon observing many attempts at creating a 'better' ventilated hive-top,
I spent a few hours last August & re-invented one for my hives.  After
inspection today, I found that two deeps & two of the three supers are
still full of honey.  2/3 of the frames were covered with highly active
bees.  This isn't the best hive I have so far for brood - as only 1/2
of  remaining super was filled with capped brood - but I'll say that's
appropriate for our climate (CO) during this time of year (no nectar
sources yet).
There was MUCH less junk to clean out of the bottom board - and a much
cleaner hive throughout (mildew, dead bees, chewed down frames, etc.).
The difference between this hive & the 18 or so others at the same site
was obvious - with the other hives clearly showing they had weathered
the winter. (Note - this is the only hive I left all the supers on last
fall - perhaps the insulating value of the honey was enough to keep the
bees comfortable?).
 
The hive top is really just a box, which I constructed of 10" x 1"
lumber - leaving  2" to telescope over the hive-sides.  The inside cover
was fitted with the standard-oval opening - which I used hardware-mesh
to make a tube-shaped funnel for outside bee-access through a hole
drilled on the outside surface.  Above and around the mesh, I placed
fiberglass insulation & cross-drilled four holes on opposite sides -
drilling up so the rain/snow wouldn't easily enter the box.  Another
piece of wood sealed off the top with approximately 7" of insulation
between the bees & the outside.
 
Rather heavy piece of equipment when I was through - but I think I'll
try several next year to give a better 'trial' of the idea.  Lot's of
variables may have had a play in this hive - new queen, race of queen
(NW Carniolan), placement of hive, somewhat mild winter (so far - though
we did have two solid weeks of -20F temperatures), amount of available
stores, etc...
 
We live in rather arid conditions, so types of insulation to fill the
space in the box may need to be accommodated for your environment.  I'm
thinking even common styrofoam peanuts may provide a good deal of
weather-resistant 'ventilated-insulation'.
 
If other people have tried insulated tops with ventilation - please post
your views on the subject.
 
Happy Keeping,
Matthew Westall in Castlle Rock, CO