I know what you mean, but you can't really get a good view of what's around so you cant say it's small per say yet
i'd imagine some perks like local leader increase the size you can make a settlement/house, or different areas allow for larger ones or something like that
and sorry but you just arent gonna get an unlimited build option or super mega structures with armadas of turrets and lightshows and blah blah on your plot.... thats a bit silly
they have the rest of the game's stability in the area, npcs, scripted raids, etc to consider, plus the building/settlement feature is just a side thing that simply can't take too much umph from everything else
put enough crap in a little area and you get stuttering and crashes (but im sure there will be a mod that removes it/adds larger plots for the pcs that can deal with it)
but its a necessary evil, a teeny tiny necessary evil that shouldn't bug you unless you are WAY too picky
it's not a city sim, so the city building just can't be what you seem to want
i don't go play sim city and get whiny that i can't go first person to the 14th floor of a building and pick up a clipboard off a desk
all i can say is play a city sim between fo4 plays if you want that experience, otherwise shrug it off and deal so you can enjoy the game without having a sour note in the back of your mind over a pretty understandable game limit
orrrrrrrrr mods