Constructing a safe is not a DIY-er project.
Also, "plans for the internals of a vault door" will not help you build a safe. Vault doors and safes are two completely different things. You will have a hard enough time finding specs for safes, let alone a vault door.... Even within the safe & vault industry, vault info is not just given out to anyone. There are only a handful of people in this country with access to the information you asked for.
That being said, I will offer my assistance in any way I can. Safe locks are available on eBay. Other, more hard to find parts like relockers and boltwork I may have lying around my shop and if not, I can order it for you. If you have trouble with a certain part of the build, I can scan relevant parts of my literature, but I'm afraid I can't just scan entire tech bulletins and post them.....
Already, I can say that if you are planning on just welding some 1/4" steel onto some framing, you aren't building a
safe. You are building a lockable cabinet or strong box, at the most. The easiest way to explain the difference is that a real safe is SOLID... Whether its steel, or composite materials... There are no seems, welds or fasteners on a real safe.
There are safe-building lessons to be learned, and safe mfrs have had 200 years to learn them. It's not as simple as you may first think.
If I can make a suggestion.... Look around at scrapyards for broken safes. A simple ex-government of canada plate safe that needs work can be had VERY cheap. You can then make repairs to the boltwork/door/hinges, replace the lock with one of your choosing, beef up security (add a high quality bit key lock, glass relocker, etc), add shelving and do the cosmetics (paint, etc).
I think you'll be a lot happier with the end product, this way.
Safe restoration is actually a hobby to most locksmith/safe techs... Because you put a LOT of time and money into it, usually its not financially viable to restore safes for resale (the exceptions are antique safes and vault doors).... But its fun and rewarding. I'm actually doing some customization on an Inkas ST-2154 right now... Adding a german high security bit key lock, swapping the group 2 comb lock for a type 1 electronic lock w/biometrics, and a few other neat tricks. Its fun, but time consuming.