Hi, it is a great opportunity. Especially if your relationship with your parents is a good one, otherwise things can get messy. Without knowing the real estate market youre in, I would suggest to speak with your parents about the monthly expenses. There is the mortgage, the monthly maintenance-condo fees, the owners and renters insurance you have to keep etc. So what will be your monthly expense and what happens if the person who rents the room fails to pay or leaves etc. As far as the mortgage goes. Im not the pro on this subject so I hope someone with more information answers you but I don't know why you would get a better interest rate than them. I understand property tax discount purposes but your monthly income and income/dept ratio can be the determining factor for your interest. So that's why I was confused but like I said Im not too knowledgeable on this. Sorry