I have just come across this post so here we go, naturally bees will use a cavity, this will be approx 18" x 18" and will expand vertically or horizontally as it does not matter which as all they want is warm and dry!
From the video they are extolling the horizontal method where the bees will expand there wax combs as they build up from the Spring and this method has the advantage of being accessible in the flat direction so that combs can be removed without have to lift heavy boxes of combs vertically. This has advantage for older persons or disabled. A disadvantage is that the horizontal hive stands on 4 spread legs and is easily blown over as it's C of G is high. Also it is not easily moved taking more space etc.
Traditional beekeeping has nearly always been in the vertical so you add boxes and the bees will also expand the wax and combs, but in boxes that are easily transported and manipulated, I am an exponent of the vertical method in National Hives. There are others like WBC's and Commercial hives but even I cannot lift a box weighing 60lb easily.
Beekeeping is a personal thing and the choice is one you live with as if you have 2 or even 3 types of hive you have to source equipment for all 3 types, ergo, better stick to one type of hive as it can be expensive.
Now, all wood hives should be made of Western Red Cedar, but of late some white wood hives have appeared and they are cheaper but will not last as long. basically buy a flat pack brood box and shallow boxes with a base board and a Crown board and a roof. then get your bees. One very important thing that novices never take into account is bee space, that s that bees will fill any space over 5mm with brace comb. Hives are built in such a way that bee space is included in the make up and measurements. I often have to break down a hive and rebuild the boxes as they have no bee space.
A novice beekeeper has very little knowledge of bees, their ways and actions so it is better to have a person with some experience to mentor while you learn. Never take all the honey, leave one box above the brood box and that is the bees reserve for a harsh Winter/Spring period.
Look on bee keeping as a philanthropic hobby, but if you go commercial then you will need to engage in the sale of beekeeping hardware and engage with customers and the beekeepers who may have more experience than you. There is no money in just taking honey and selling it as the overheads will kill it dead. A Gross of 1lb jars is £75, A hive complete empty, flat pack will cost £350 in Cedar. Start small and the bees will build up slowly. At one time I ran 15 hives and it took all my time, I now run 8 hives and make a reasonable harvest and sell locally. Farm shops etc. Remember you have to conforming to labeling regs. and weight conformity and origin of the honey by law. Hygene is also on the list as if you sell honey they can inspect the processing place and it has to be separate from any other food process.
Sorry, long post but needed it seems. Clive I am happy to expand explanations if needed so please ask.