I assume you mean you rented "OUT" a room in your house that you own, and did not "PAY RENT" for a room in a house you do not own.
Read the screen. Pay attention to the small print. Your percentage of business use for the portion you rented out is one hundred percent. From the time you converted/declared the space as rental property, it was one hundred percent rental use. What is was used for before you converted it *does* *not* *count* for anything. So your business use percentage "of that specific room" was 100%.
