To begin with, the air is thin, so plan to take an hour or two. Location is everything: you want to burrow into a nice bank of snow, not one that is going to drift over, and definitely not one that is in the possible path of an avalanche. So we have opted here for a sunny col. This will have other problems.
You will need at least two people. First, dig out an entrance, as shown above. Then one shoveler gets inside and begins to chop out a main room, shoveling snow toward the door where shoveler #2 chucks it out on the windward side of the entrance. This is hard work, so rotate positions every 15 minutes.
When you have a room of 8 feet by 8 feet dug out, with 7 feet of head room, send one person up on top with a long avalanche probe or tent pole. S/he must poke that pole down precisely through the middle of the ceiling in your main room, to create an air hole. If you can protect this air hole with a tube of some type, that’s even better. Tamp down the roof area gently, then get off and stay off.
Inside, create sleeping pods off the main room. Make these about 7 feet deep, 4 feet wide and 3 feet high. This is bigger than you will need at first, but the entire cave and all the pods are going to SHRINK the longer that you stay in them. Your body heat is going to cause some melting, and that will make the snow compact and come in towards you. The sun outside and on top aids the melting, but you won’t see it. At this elevation snow evaporates without ever becoming water. An unsettling feeling.
Set up a cooking alcove in the entry way. You don’t want that heat inside, or the cave will shrink even faster, overnight. Best to establish this on the windward side beneath the excess snow you mounded up. Make sure it is protected from drafts.
Figure out your inside lighting. Lay out your ground cloth. Get used to feeling slightly claustrophobic. At night you will wake up in your mummy bag in absolute darkness and not know where you are: your sleeping pod will be shrinking, and after 3 nights you will feel it on all four sides, creeping in. That’s when you know that in the morning you have to go up or down.