What would you do/upgrade/etc. when building an underground bunker?

Atlas bunkers had some decent upgrades/features I'd like to incorp into my own.
I've got the basics such as air filtration, etc. but looking to dive into the more nitty gritty details.

Anyone have any good old military PDFs that cover thickness, door features/locking patterns, etc? IE. Are top/bottom bolts on the door better than Left/right side. Things like that.. I am curious to know. Best material to prevent thermal…

Bunker Specs