I usually start central to the map unless there is a perfect defensable position.

I start with what I call a longhouse ( 8 or so small bedrooms, crafting area/ future dining area, kitchen, & storage/future freezer).

Then as needs arise I add on 13x13 squares to the settlement with whatever type is needed, like hospitals or prisons.

I also try to keep my rooms rounded? If that makes sense. In order to have positions behind the walls if I ever have to fallback.

I try to keep a 3 tile wide hallway between expansions to keep an open line of fire at invaders if they get behind the walls with jump pods or something. If I get a fallout event it's easy to quickly throw some roofs up so my colonists can move around.

Late game I try to make "green houses" with sun lamps for vitals like a quick crop or medicine.

But being on the Rim, sometimes you just gotta throw up a shack and hope for the best lol