Here in the SW part of the country, tends to get hot and dry during the summers. Was thinking of building a short box, 3" or so tall, that have 1.25" holes drilled in each side, screened, and placed on top of the inner cover on the top super. But then was thinking about rain blowing in and ruining the inner cover and draining into the hive. Guess rain blowing in is common in a feral tree hive, but looking for opinions here as I am new to this.
Bees cool the brood by placing water on the caps and fanning to evaporate it. In general they can fan enough air through to give them the ventilation they want. If you provide too much movement of outside air into the hive, the brood will rise to the ambient air temp. which might kill them. Better to let the bees handle it.
Too much ventliation is as bad or worse than too little. Ideally, a properly vented hive allows a small amount of air to enter from under the hive, flow up the front wall of the hive, and out at the front of the hive.
The simplist way to accomplish this is to use a screened bottom board and either an inner cover that is notched on one end (1/2X3/8) or an Imirie shim with the notch to the front under a migratory top.
You can actually slide one box back and leave a 3/8" opening and the rain will just run down the front of the hive. It's actually not a problem.
You can do a modified DE hive. Get ventilation and be able to feed 4 qt jars at a time with the same top cover. The ventilation holes are angled to keep out water. Mine are. I made them myself. They are cooler due to the air space. They cost a little more to make, but I feel they're worth evey penny. Not to mention they look nice.
JD