"Una habitación está disponible." (from exercises)
It is not quite clear to me why is here ´está´ and not ´es´. Reviewing estar/ser usage in my notes, I have not found the answer. Is there anyone to make me clear this?
In this case, you use "estar" because the sentence is talking about the CONDITION of the room. In general, "estar" is for location, condition, and feeling. "Ser" is for origin, time, and description. There are some exceptions to this rule though!
SpanishDict (http://www.spanishdict.com/grammar) has a very good explanation of Ser vs Estar.
Estar, remember PLACE, it is for: P: position L: location A: action (used with gerund) C: condition E: emotion
Ser, remember DOCTOR, it is for: D: description O: occupation C: characteristic T: time O: origin R: relationship
It helps me a lot, hope it will help you too