What for? It's luck involved. They seem to like wide spaces like 30x30x3 just over bedrock. Lava isn't a big factor but they seem to spawn regionally. If you don't find them at your base dig 50 - 100 block further an try again.
New user here. I have problem, the wiki doesn't work for me. When I click on a link (like those in the OP) it opens a not fully loaded version of the forum, not the wiki. To access it I have to use google cache (but then there are no pictures).