Custom Structures with mobs

Hey guys
Is it possible to make a naturally generated structure that spawns its own set of mobs? (not from spawner)
I'm planning to make a dojo and I want it to spawn skeletons with a sword with a katana custom model
If so, is there a video tutorial for it? I know I can simply search it myself but I want it to come from y'all because y'all know what's best
Thanks!