The question Does anyone know free DIY ultralight plans? has been closed as off-topic, but there are no reasons given for this. I don't necessarily want to challenge the decision, but it would be useful to have the reasons, if only so that I and others don't repeat the mistake
This is the problem with broad close reasons, they're not very specific. You have to follow a couple of links to the on-topic help and then you will see one of the off-topic guidelines states:
Where to buy a specific part, "Which headset is the best?", Where can I get a feed of flight-related data? etc.