Today I made my first brood box from insulation-grade styrofoam sheets.
Tomorrow I'll put it outside, put a plank on it, and load about 50 kg of bricks on top of it to see if it would have carried the weight of a full hive. I'll also leave it out all winter to see how the duct tape fares against the weather. I'll post pictures tomorrow.
I learnt today that styrofoam is very, very sticky. I also learnt that the best way to cut it is by using a handsaw. I suppose a hot wire would have worked too, but I don't have one. A hot knife is no more effective than a cold one. I also learnt that you can't be very accurate with dimensions. The hardest part of the entire build process was wrapping the inner parts with plastic film.
The hive is 530 mm square, and I used 40 mm thick styrofoam. You'll notice that there is no beespace above the frame ears -- that is deliberate, so that the frame rests also carry weight. Cost per brood box: EUR 3.00.
The polystyreen sheets weigh 11 kg per m3. The polystyreen hives bought at bee stores weigh 90-120 kg per m3.