Depending on the style of Brotherhood of Steel outpost, you could do several different types of settlements for Brotherhood.
Main Headquarters:
- Large central building with computer terminals, made of concrete/brick and heavily fortified.
- Large "Vault" (Vault like a bank vault, or heavily defended high security vault to store high valued things).
- Verti bird landing area (Enough for several of them at once)
- Excessive amounts of Antenna's and communications, (maybe even a seperate building for the communications with computers, etc.)
- And of course, large thick walls and excessive amounts of heavy turrets like rockets, and mini guns
- And of course what BOS HQ wouldn't be complete without a Engineering/Garage dedicated to Power Armor? 10+ Power Armor units with all the tools required to upkeep, and maintain.
- And to top it off, a nice large Armory for weapons, ammo, explosives, etc.
(Oh, and if the area is large enough.. Perhaps even a very large metal structure for where the BOS Zepplin would "dock")
Sprinkle in tons of flags, spotlights, and wired fences, and you got yourself an awesome BOS HQ.
Smaller Outposts or Settlements:
(Of course every BOS outpost needs tons of spotlights, turrets, and flags, and some form of defense in the shape of walls, so I'll leave those out of the list since they are a given)
Forward Communications:
- Lots of communications devices, and heavily fortified bunker like look.
Training Barracks:
- Shooting Ranges
- Armory
- Vertibird landing area
- Lots of sleeping area's with Cots and bunk beds in a row.
Forward Outpost Base:
(Something like where they stage patrols, missions, etc. from)
- Meeting room where missions are explained and given to the soldiers. (A map on the wall, filing cabinets, and chairs all in a row looking at a board, with a large table in the back)
- Armory
- Vertibird landing area.
- Sleeping area.
- Power Armor area for maintenance.
Random other ideas:
- Intelligence HeadQuarters.
Makes sense for the BOS to stage a central location for their intelligence. Since lore wise they are just getting to the Wasteland, and want to be gathering intelligence on everything.
Could have one large heavily fortified bunker system.