From my experience it's entirely up to you. What I did w/ my red trapdoor spider is I started three burrow sites. I put holes in the substrate maybe an inch deep tops and wide enough for the spider to get in to it. After about a week it built it's burrow in one of those sites and used the cypress I put in there to build its trap door. Even if I hadn't started its burrow it still would have made its own burrow.