[2022] Room Tier issue

Singular angled roofs do not count as finishing a room, as the room feature also checks for diagonal air in determining if something is closed. You can work around that by making diagonal roofs two blocks thick or by just placing a flat roof below. While this does work as intended, we plan to revisit that later in development.

Originally posted by stlyau: I never said it wasn't working as intended. It's just not something that is mentioned in a tool tip or on the Eco Wiki.

I was actually answering the OP directly, hence wasn't in any relation to your post at all. Sorry if that wasn't clear.

Basically you will always need a full rectangle, e.g. diagonals need to be filled.

Eco has a lot of useful information in its tooltips, always worth to check those out.