I build all my own woodenware except for frames because I can build it for about a third of what you can buy it for out of the catalogs. I am not happy with my inner covers though, I built them out of masonite and just tacked and glued a rim on both sides, and cut the elongated hole in the cover. However the masonite soon warps when put on the hive so what you end up with is a bow either upwards or downwards and creates problems. If it warps upwards then the bees have a hard time accessing the top of the cover (because of the larger bee space) for when I feed an inverted jar. If it warps downward then the bee space is virtually nothing and the bees cannot cross the tops of the centermost frames with the inner cover on, also when you put the inner cover back on after doing an inspection it will crush a bunch of bees.
For those of you who build your own inner covers, what do you build them out of? Looking for something that will not warp to eliminate the problems I am having with mine. Thanks. John