I prefer to leave the screen off the inner cover holes. If the bees don't have access to that area, all kinds of spiders, ants, roaches, earwigs, etc, etc. take up residence in there. They also seem to propolize the screen. I have never had any build comb in the vent box.
The vent boxes from bee works have the holes drilled at an angle to prevent rain from getting in, and they are positioned so that you flip the box over for winter and the telescopic cover covers the holes.
I have since just built the boxes with the holes drilled straight as the telescopic cover provides protection and I just shove a piece of insulation in for winter.
You may want to consider a more simplistic design if you intend to build many. If you only have a couple, then design away