I haven't done this for roaches but works great to keep the humidity up for tarantulas but ventilated, too.
I got a piece of plexi-glass cut (any local glass place can do it) to sit in the rim of the tank but only covered about 2/3 and then put the screen over that to prevent escapees. You can regulate the ventilation by removing the plexi all together or running a fan above the tank to keep the air moving. For my arboreal T (she was in an upended tank) I got a piece to cover the whole front(top) and drilled .25" holes in the top 2/3 of the plexi. If you drill the holes be sure to do it before removing the adhesive paper it comes in to prevent splitting. Also, bring a good template for them to cut so you have a tight fit. Even in Rose's upended tank it was a good enough fit that didn't fall out. Oh, and have one corner cut off at an angle as a finger pull to remove.
lele
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0.1 veiled - Luna
0.2 felines - Kyndra and Líta
1.0 African Clawed Frog - Skipper
0.5 Mad. Hissers
0.1 Chilean Rose Hair Tarantula (no name yet)
?.? Goliath Bird-Eater Tarantula (no name yet)