Οροφή can refer to something like the sun roof in a car. Σκεπή is also a common word used to mean roof of a house.
οροφή = στέγη = the top of the building/room, e.g. a roof but it could be flat
σκεπή = roof in an inverted v shape
το ταβάνι = the ceiling
When unsure about such terms with overlapping meanings in either language, a good rule of thumb is to do an online image search. The images that show how the term is most commonly used will be clearly the most numerous in the results.
The drop down hints are like a dictionary. Not every definition is correct in every sentence. It's usually the first word that fits in each sentence.
This sentence has "roof" and "ceiling" as definitions not "shelter". If you saw "shelter" it is a computer bug. Please take a screenshot and report it. https://support.duolingo.com/hc/en-us/requests/new