I find black holes as Gargantua, are a danger to the public. Everyone who happened to come by, can fall into it. So I built a cage for Gargantua.
Realistically speaking a structure of that size is so improbable it borders on impossible. Also caging a black hole would do little to stop it's gravitational pull, so at best you might end up with a lot of junk stuck on the shell of your sphere.