A suitable house is a place an NPC can use. It is not a command that summons whichever NPC you want. When the room passes Housing Query but stays empty, stop rebuilding the walls for a moment: vacancy and character requirements are separate checks.
Use the housing message to choose the next step
Open the housing menu and use its query tool on the room. If the game identifies a room problem, fix that specific problem and query again. If it says the room is suitable, move on to the resident assignment and the NPC you are trying to attract.
The official housing reference describes the size and furniture checks. A normal room needs at least 60 total tiles including its frame and fewer than 750, with suitable lighting, comfort and surface furniture, and an entrance. A work bench can fill the surface role; decoration alone does not substitute for the required categories.
Make one simple room easier to diagnose
For an uncomplicated starting shape, a rectangle nine tiles wide and seven high has an outer area of 63 tiles. Add a solid floor, a door, ordinary crafted wood background walls, a torch, a work bench and a chair. Keep clear standing space inside, then let Housing Query judge the result.
This is a troubleshooting starting point, not a guarantee that every room with those outer measurements is valid. Furniture placement, the standing area and nearby evil biome conditions can still matter. Build and query a plain version before adding a complicated platform floor or subdividing it into tiny rooms.
Background walls are a different layer from the solid blocks around the room. Natural-looking scenery behind the player is not proof of safe housing walls. Ordinary crafted wood walls avoid that ambiguity; some special wall items are unsafe, so “I placed it myself” is not a universal test.
Check whether somebody already owns the room
Use the housing menu’s resident flags rather than judging vacancy by whether an NPC is physically standing inside at that moment. A resident can be elsewhere while the assignment remains. Most ordinary town NPCs need their own room; pet exceptions do not turn one room into unlimited town housing.
Test one NPC requirement you can actually verify
For example, the Merchant needs the coin condition as well as available housing. Carrying one gold coin is comfortably above the 50-silver threshold; money left in a chest or Piggy Bank does not satisfy the carried-coin requirement.
If the intended resident is someone else, check that NPC’s own arrival conditions. Meeting the Merchant’s requirement does not unlock every shopkeeper. Having an eligible character, a vacant room and suitable conditions also does not mean an arrival must occur at the exact instant you finish the room.
Once the room passes, preserve it while checking the remaining requirement. You will learn more from changing one unmet condition than from repeatedly replacing a house the game has already accepted.