Spengler is the official trade name in Germany (and maybe some other countries) for metal roofing. I’ve watched this channel grow up on Youtube, and wow they have added a lot of content! Metal roofing and standing seam, are codified by law there. This means everything last longer, there are fewer repair and maintenance cost. And on the market side: it means everyone has to play by the same rules, much like a bar or medical association. They study and master the techniques in secondary school. This is miles above “on the job” training, or even union training here in the US. Since union training is still focused more on meeting the “market” production demands.