I have 7 tiger barbs in my 20g, I want to make them a cave. Can you please help me out what to use and how to make it. I want lots of inlets and outlets.
Agreed with what Fluttermoth said - it tends to be only bottom dwelling fish that will go anywhere near a cave.
If you want a cheap and cheerful option, you could do what I did which was cut a coconut in half and then hollow it out. Looks great if you attach some plants on top. I have an anubia on top of mine