It's more like "I build a bridge blue print for free as an hobby project". Which is ok. (As long as you don't claim that it's something it's not.) And it's al

It's more like "I build a bridge blue print for free as an hobby project". Which is ok. (As long as you don't claim that it's something it's not.) And it's also ok for a company to actually use your blueprint (ignore copyright for a moment). The problem is if a company uses the hobbist blue print without verifying that it fulfills necessary requirements, like being safe in case of an earth quake.