"It is a room."
Maybe if someone is asking about a term they're not familiar with? An example I can think of is maybe something like:
客間って何ですか？ (What is a parlor?) へやです。 (It is a room.)
Somebody might say this to a foreigner who is learning Japanese by pointing and asking 何ですか？
It can be: "ここはへやです" where ここ means "here." If the context is clear this can be omitted.
The particle is used when saying about the room itself likr "This room is..." or "In this room there is..."
Guys best way to remember this one is imagine waking up to outkast singing " HEEYAAAA WHOOOOHOOOOH"in your ROOM :D