Build or buy? That is a difficult question to answer for many of us who have tool-intensive hobbies. If you need a box and pan brake to be able to make some parts for a project you are working on, you may have had the thought that you could just build one yourself. Can't be that difficult, right? Maybe - maybe not. But there are other things to consider as well.
I knew a guy once - worked professionally as a luthier. One of the last things he had to do when finishing a violin, was to put in the tuning pegs - made of solid ebony. These need to have a conical shape to stay put in the peg-head, and this is achieved by means of what looks like a giant pencil sharpener. Now, this thing costs around 200 dollars, and when his father (also a luthier) heard that his son had paid that much money for something so simple, he set out to build one for himself. The thing is - he managed to build one in around two days, but he got nothing else done during that time. The big question was - how much was his time worth to him?
Drill Bit Sharpener
How much is your time worth to you? If sheet metal work is your hobby, or you have a hobby which requires you to do sheet metal work from time to time - do you really want to take part of your precious spare-time and devote it to tool-making? For some, the answer is no - given the chance to reflect on it. For others, tool-making can be as much fun as building anything. If you belong to that last group of people, then, by all means, build away!
Lots of people have built their own sheet metal brake because they needed a fast solution for bending sheet metal - but did not feel they could justify buying a sheet metal folder just to make a few bends. Some folks even go as far as building their own cnc-routers to use in their work, but then factory-made cnc-machines can be very expensive indeed, so at least it makes sense from a financial standpoint. But the thing is - a regular sheet metal brake is rather simple. It is, at its most basic, not much more than a vise with a few bells and whistles. A box and pan brake is a bit more complicated - but not much more expensive to buy, than a sheet metal brake - so while you could put the latter together in a few hours, the former might take significantly more work. Why? Because there are more parts, because the functionality is different and because it requires a bit more thinking and planning. In the end you have to decide whether this is something you would enjoy doing, or whether your time is better spent doing something else.