I took two of the Covenant houses and re-textured them to look like "stone" cottages (set 1) or "brick cottages (set 2). I also added them to the workshop build menus as constructible items, which can be found in the "Wood"/"Prefab" section.

They are FULLY NAVMESHED inside... I tested them and they all work with the npc's...

To add doors to the houses, you're going to have to use a "place anywhere" type of mod, since I really didn't spend an exorbitant (big word) amount of time to add some snap points...

You will need the "Place Everywhere" mod for this... Place Everywhere at Fallout 4 Nexus - Mods and community (nexusmods.com)

Like I said, "simple mod". Enjoy...

Oh... Almost forgot... Just the base game is required, no DLC's needed...

Almost forgot again... Install with your mod manager...