How do you unlock professor quirell on lego harry potter wii?

To unlock Professor Quirrell in LEGO Harry Potter for the Wii, you need to complete the "The Philosopher's Stone" story level. Once you finish the level, you will be able to purchase him in the character selection menu using studs. Make sure you have enough studs accumulated to unlock him. After that, he will be available for you to play in free roam.