Once I had explored the entirety of the Vault 88 caves, fetched all the things, killed all the things, experimented on all the things... and it came time to build a vault of my own, I felt the need to see if I could link up as much of the available space as possible into one single vault structure. What you have here is the blueprint for what I produced. 

I decided to keep much of the original construction equipment and build around that, so you will find many of the piles of junk, the diggers and the trains still in place (although some have been moved with console commands). The theme is that the vault is still in construction and expansion, with areas being excavated and others waiting to be expanded into the space. 

Every area of the main cave space is visited by this vault.
The areas that lead into the exit areas at Milton General and University Point have been sealed off with doors (that I personally keep locked with console commands) and nothing is built beyond those.
Every area of the vault is linked together and is all powered by the original generator. 

I've used console commands to force the vault pieces into places that they can't be snapped into and this has allowed me to wind my way through the "narrow" passages that snapping doesn't allow you to use, and build all the way up to the cave ceiling in the main area (above the girders).  
I've taken great pains to hide all clipping of the rock walls into the vault interior, or to incorporate the rock walls into the design. 

The vault design is very twisty, with many routes from one area to another. Some people may not like this as it can be easy to get lost. But I do have signs and directions posted up to aid navigation (you have no idea how often I got lost while building!). 

There is room to add to the vault structure in some places, while other areas are packed in from wall to wall. This build did push my system to it's limits to render, so I stopped where I did to avoid crashes (I would have liked to have really filled all available space, but not to be). 

Settlement stats are: 
32 Food
100 Water 
152 Power (with one bike in use)
34 Beds 
204 Defence (with not all guard posts occupied) 

This blueprint will add 8289 items to Vault 88. This will impact your fps (depending on your system), and may take quite a while to import. 

This has been exported with Transfer Settlements 1.41 and now includes all the wiring. Send some love to CDante for getting this working as it makes complex settlements like this work straight away without you needing to do any work.
This will be installed in slot 10 of Transfer Settlements by default. 

It's recommended that you scrap/store everything within the settlement first and use the option to include "original items". Some of which I kept and moved, this will lead to you having overlapping copies of those items if you don't remove them first... 

This was built with access to all the DLC, and uses many mods to complete the structure and decorate it, which you will need if you want everything shown (see below for list). 

My settlement walkthrough can be seen here (in 4 parts): 
 
 
 
 

DLCs required: 
Wasteland Workshop 
Contraptions  
Automatron 
NukaWorld 
Far Harbour 
Vault Tec

Mods required for full recreation (minus texture replacers):
Transfer Settlements by cdante (Including all the requirements for that mod), 
Homemaker by Nova Coru, (Important) 
Half Width Shack Walls by CitizenRandom (Important) 
Craftable Balcony Supports by DarthWayne (Important) 
Settlement Objects Expansion Pack by ccmads (Important) 
G2M Workshop by g2mXagent and keppekinosha (Important) 
Concrete walls with window glass by cartman1975 (a few walls in certain places) 
DDP AIO Standalone by ddproductions83 (Important, "Cookiepocolypse" may work instead) 

Snap 'n Build by ad3d0, (Minor) *
*Good News, everyone! Snap 'n Build is now back on the Nexus. This was built with the previous version 1.9, it should be compatible but let me know if there are any unexpected results. 
I tried to avoid it's use in this build so I can't imagine what has been used, but you shouldn't miss it. 

Snappy HouseKit by robboten (some minor pieces) 
CWSS Redux v2 by FLipdeezy (sinks and bathroom items, Important) (not currently available on the Nexus, I'm looking for alternatives for the future)
Some Building Stuff by Quaz30 (Important, random decorations, hiding rocks) 
Box Houses by  Ethreon (for a few walls) 
NorthlandDiggers Resources by ludvig08 (Important for all the jobs for your settlers and the themed rooms of the settlement)  
Immersive Vendors by Xgrufijury, (Not sure if you'll get vanilla shops in place of these if you don't have this) 
Better Cooking Stations by steve40 (Like above, not sure if you will get vanilla versions without this) 

OCDecorator by McFace, (Important for small decorations) Also requires the DLC version. 
Old World Plaids by LupusYondergirl (Seats, Tables, Curtains and rugs. Important)  
Working Table Lamps by FrauZockinsky (for lamps, not vital)  
OSHA Unapproved Safety Signage by BlandSauce, (for signs, not vital) 
Business Settlements by Tamayo831, (for signs and shop items) 
Better Stores with the farharbour esp by blazeda59 (for shop stuff)  (not currently available on the Nexus)
Do it Yourshelf by dinozaurz (Important for filled shelves), Plus the "extra Ammo" add-on. 
Warehouse Shelves for components and ammo by Cartman1975 (Important for the various storerooms to not be empty) 
Lore Friendly Posters by Dhegonus (for posters, not vital) 
FAC Paintings by Foggypath (Pretty paintings, not vital) 
Minutemen Morale Pack by EvilViking13 (for minutemen propaganda, not vital) 
Craftable display Shelves by Elianora (for display shelves in player room) 
Eli's Craftable Flower Pots by Elianora *Has been included with Elianora's Fallout Junk Yard. Check the files.  
Vertical (wall-mounted) power conduits by Daedragon (for a couple of terminal connections, not vital) 

Check the mod page for Transfer Settlements for more information about how these blueprints work and for any issues with importing settlements. 

Thanks.