Four Gold Bricks can be found in the Leaky Cauldron basement. To get there, destroy the padlock with (RD).
NOTICE: You have to complete all 24 Hogwarts Crests before being able to begin this task.
Once you're inside, just build four statues (WL) for each completed game year.
Destroy the cage with magic and then use (WL) to create a small cleaning machine. Mount it and clean the whole store out of dust. The brick will appear by the seller.
12 Gold Bricks can be bought at Eeylops Owl Emporium. The total amount of studs required is 6 600 000.
Hermione (Ballgown): Madam Malkin's - use (WL) on the clothes scattered throughout the floor.
Harry (Tuxedo): Madam Malkin's - go up the stairs to the changing room and choose the one on the right (the occupied one).
In order to get to Knockturn Alley, you will have to use (RD) on the gate opposite to the Eeylops Owl Emporium.
Right behind the corner at Borgin and Burkes.
Igor Karkaroff: The token is very visible, build a staircase using the planks (WL),
The Bloody Baron: Jump onto the cart, aim at it and shoot yourself into the air.
Shifty Wizard: Destroy the chest on the table and then stand on it. You will be thrown into the air eventually.
Lord Voldemort: After collecting all 200 Gold Bricks, create (WL) golden door #1 and play the bonus level - Harry's Destiny. Your task is to collect one million (1,000,000) studs #2. You can't use multipliers. Smash everything you come across - get into the vehicle to speed things up.
You will find purple studs in the sewages - you will also get one for destroying a hydrant.