Yeah, the angled thatched-roof looking pieces (and upgrades you get later) are all that count as far as I have seen. In particular, you can't use floors as roofs. Gotta put a roof over the bed, and maybe a few walls. Certain game functions require an object be sufficiently "covered"; that includes using crafting stations too. And you need a fire nearby to sleep. There are rules... I had to stumble through all this stuff when I started out too. But it is part of the fun :)