What are some fun building hobbies?

Try making origami. It’s a pleasant building hobby to increase concentration and brain health. The result leaves you satisfied, so it can be a great way to relieve stress.
The great thing is there are lots of resources to help you get started. You can use origami applications or books. In my opinion, it’s best to start with The Complete Book of Origami: Step-by-Step Instructions by Robert J. Lang. You may come across printable origami on the internet. But it’s best not to use them unless you need to make something complicated, like a dragon!
You can also try kirigami. It’s similar to origami but involves cutting and glueing, unlike origami. I don’t have much experience, but it could be fun.
Woodcrafts can be fun too. It’s a little more expensive than the other options; you may need to buy some tools.