PC House not valid, but why?

[Mr.Moe]

a picture tells more then a hundred words:

http://imgur.com/KAjjcpW

First floor: Valid
Second: Not
Third: Valid
Top: not valid ofc

 

[Ezel]

Top: probably because there's no light and furniture.
Second: No idea. Try adding a torch on the left side.

 

[Arekusei]

Because of fences you put. Also right from fireplace not completed wall.

 

[critcodedtuna]

Quoting the wiki:

The NPC needs at least one solid (non-platform) block to stand on at night. This block may not be directly adjacent to either of the side walls of the house.

Replace one or more of the platforms with a solid block and it should work.