I learned early on not to build a settlement on the ground. Between bodies lying around (on XBOX1 console, you can't sweep them away using brooms, like PC players can), and the grass poking through the floors (irritating to me) and enemies sometimes getting through defenses to walk right into buildings (that happened to me once and I lost a settler), it's just better to build up. I always start with the floor that has a ladder attached to it. That's my basic foundation at the majority of my settlements (I actually used the houses at Sanctuary, The Slog, and Taffington Boathouse, but everyone else was a build up situation for me). As many people have pointed out, Fallout's build feature is unrealistic in that structures can be suspended in the air with just the ladder in place, but this 'cheat' it makes sense, given the build limitations. For that reason, I overlook the gravitational impossibility.
In any case, after that initial ladder-floor goes in, I build a second floor off of it. The second floor is always for a dining table or two, and a living room with couches, side tables, some plants, pictures on the walls, rugs on the floors, a cigarette machine, and a radio. Lots of lights. That's the settler's main lounging area, typically, as it satisfies much of the their needs for seating & basic entertainment (they stop saying, "my feet hurt, my back hurts, everything hurts" and "work all day, nothing ever changes" when you make this a good place for them to gather).
The third floor is bedrooms and the bathroom (complete with privacy wall to screen the tub, a box of Abraxo, a metal or enamel bucket, a dishrag, a hairbrush, and a bar of soap, all stored inside a small container in the bathroom. I never put in a toilet, as it's unnecessary for their happiness, but the tub and soap ARE necessary to get them to stop complaining about having dirty fingernails). In the bedroom, I typically stack their beds end-to-end or in rows with a bit of room on all sides between each bed. I throw down at least 1 container for their clothing (storing casual, non-combat clothing in here seems to up their happiness rating as well).
On the top of the roof, I place level 2 machine guns all around. The height advantage allows the guns to find enemies further off, which alerts your settlers well in advance as well. Usually, this structure is tall enough that I put my engines on the roof and connect them to either towers or wall outlets & string the wires along the outside of the building. This is also the place for a recruitment beacon, if the settlement is large enough to allow for more bodies (like Spectacle Island and Kingsport Lighthouse).
Obviously, this is just a standard template that is modified, depending upon a specific settlement's space requirements & needs (for instance, at Kingsport Lighthouse, I have a metal wall going across the whole front of it, with a small space in between for settlers to go in and out. Gun turret towers sitting on the tall walkways are placed behind the metal walls, facing out, so they can get at any direct assaults. Gun placements are also on the top of my settlement roof, facing the other 3 directions to protect those sides. I don't use the boat house or the dock area at all, but my water tank is down there with 1 engine to run it. I do use the house, too...this is where my bathroom and level 3 bar are located, along with some sofas and the cooking stove).
As for decorations... On at least one outside wall of each of my settlements, usually facing the main way in, I put up flags (U.S. flag, Minutemen, Brotherhood, and Railroad) to let everyone know it's a safe haven for all those factions (I put up the Institute flag once, and my settlers happiness went down a few points...once I removed it, it returned to normal). Inside, I toss down onto the floor of the living room and dining area a Chessboard, a globe, a Blast Radius game, some vases with flowers in them, and maybe some coffee mugs/drinking glasses, and an ashtray or two. When you go into build mode, you can pick those items up and they will rest on surfaces. Your settlers' happiness factor IS affected by you throwing down items or putting them into storage containers on site for them. If there's enough room to build pictures onto the walls, I do. The stuffed animal heads gross me out, so they never appear anywhere at any of my settlements.
Somewhere on property, I always build these (as they increase settler happiness):
- level 3 general trader stall (necessary in general to raise settlement happiness)
- scavenger rack (brings in caps & scavenged items...your settler finds these things & just gives them to you. If you pick a good scavver to assign this task, you could be hauling in thousands of caps within days)
- level 1 medical stall (necessary to get the settlers to stop complaining about having blisters)
- level 3 bar stall (necessary to get the settlers to stop complaining about being hungry/thirsty if you don't have enough food/water put down for them or can't put those things down due to there being no place for them on the settlement's grounds...also, raises their happy factor immensely)
- a trader stall for caravans (once this option opens up later in the game - allows Doc Weathers, Cricket, Lucas, Kat, Stash, and Trashcan Carla to come to your specific settlement, which ups settler happiness, too)
Optional: other stalls. The higher the level, the happier settlers are. The problem is manpower. Some of the smaller settlements don't have enough people to farm, man stalls, and go out as supply caravan routes. You have to balance those needs vs. the happiness factor.
Some settlements are large enough to allow a build of the following, too:
- a dance floor with rotating mirror ball and flashing lights and jukebox
- a pool table (collect all 15 balls + the cue ball, at least 2 pool sticks, and a rack and throw them down on the table, arranging them using the build function)
- a magazine rack (where you can store all those Grognak, Mass. Surgical, Junktown Jerky Vendor, Survival Guide, Hod Rodder, etc. rather than sell them -- this goes a huge way towards making settlers happy, too)
- a bobblehead stand (I put this in Sanctuary, since this is the settlement I most go to, personally)
- Nuka cola machines (store Nuka colas in here and the settlers will swipe them, but it'll make them happy, too)
- Ice machines (if you throw in meat and purified water, settlers stop b!tching about being hungry & thirsty all the time, I noticed...this is a good fix for settlements where putting down water resources is difficult, like Boston Airport or Hangman's Alley)
- a basketball court (you can set up the net, then place basketballs on the ground near it)
- a baseball diamond (works best at Abernathy Farm or Egret Tours Marina - put down 3 bases, a home plate, and in a nearby storage cabinet, some balls, gloves, bats, and if you're really cool, baseball outfits & hats, too)
- a kickball diamond (same as baseball diamond, only put down kickballs)
- a mini bowling alley (you can actually build this using the mini wall spacers, and setting up the pins in a triangle shape at the end. put down a few bowling balls nearby and voila! I would recommend setting it up outside on a lawn space or paved area and leaving the back end open so the bowling ball can go through & not bounce back and knock down pins)
- an outside party/gathering area (I did this at Starlight Inn, because of the limited build opportunity...set it up underneath the settlement to protect it from the weather. Put down some rugs, some couches, some plants, some tables with benches/picnic tables, a jukebox, and the level 3 bar stall and cooking stove. Put lights everywhere, including a mirror ball. Settlers love gathering here at dark).
Oh, and don't be discouraged by how small the build area is for Coastal Cottage, Oberland Station, Outpost Zimonja, or Hangman's Alley. The build up function works fabulously for these spaces. Coastal Cottage can also have that little hill to the left of the barn used for a trader area (just build metal walls around it and a roof over it and put some turrets on top and you've got a little nook for a gathering space & trader stalls). Hangman's Alley actually lends itself to walkways (using the smaller quarter-sized floors and ladders...they just hang in the air & you can put turrets on these easily). Oberland & Zimonja lets up build up to 4 floors tall, if you plan it out right.