I made this bottom board from scrap wood I found in my shed today:
I cut the thick plywood 16.5 inches wide (about 42cm) and 2 feet long (70cm). The brace wood, if you want to call it that, was the same dimensions as a super, 20 inches by about 15 inches, something like that. The hive entrance (once a hive is placed on top) is about 1 and a quarter inches high, which is fine. It’s not pretty but the bees don’t care about pretty. I think it’ll work. I’ll post a photo of it in a day or two when I put a hive on top of it. I should have been making these all along. It’s way cheaper than ordering them from a supplier and having them shipped here. If you had to pay for the raw material, though, I’m guessing it would be less than $5.
February 9th, 2013: This bottom board has worked out fine. It’s ugly and half rotted now, but the bees don’t seem to care. Today I would use thick plywood instead of chipboard, and I’d paint it, but there’s nothing wrong with getting by with one made from cheap scrap wood.
January 20th, 2015: Don’t lay this flat-bottom bottom board on a pallet or any kind of flat surface (like a pallet), if that makes sense. The wood can easily become moist, and you don’t want moisture in the hive. You want the hive off the ground, but preferably with something that makes minimal contact with the bottom board. And by “you,” I mean me.