Hvornår bruger du "rum", og hvornår "værelse"? Hvad er forskellen?

Actually I live in Danmark 4 years now and normally danish people say værelse. I can see that here in duolingo they try always to pic danish worlds that are similar to english, so it is easier to learn. Unfortunetly many times it is not good idea. In Copenhagen people use a lot english words but on Jutland not really, so if you come to Jutland and ask Hvor mange rum har i ? They would not understand.

Four walls and a ceiling... does it needs that much description ? :D

Why can't it be: This is a room?