Digging a burrow/bunker how to be safe?

I want to dig my own under ground area, nothing huge maybe smaller the 10x10ft and about 6-7ft maybe a little taller ceilings. I want to have a long tunnel reaching to it so it's more secret. I need to know how deep I should dig the room and tunnel to keep it from caving in when people or things are on/over it, or when it rains. I also need to know what I can use to stabilize the walls like wood or a certain method and how I should go about doing this. I've wanted to do this since I was a little kid and in about a year I'll be able to finally get a chance to, I want to know all I need to know to keep it safe for me and others. I don't want it to be anything super special or anything just a simple dug out burrow with dirt walls and the like, using pretty much just a shovel. Also I can't afford to put much into it like concrete and stuff like that. Any help is appreciated thank you.