~IF YOU WANT TO BE A CHEATY McCHEATERTON (like me

):
Enter these cheats (Once the Leaky Cauldron hub area has been unlocked, enter Wiseacres Wizarding Supplies in Diagon Alley. Go upstairs, talk to the vendor. From there you can enter the cheat codes.):
Carrot Wands AUC8EH
Character Studs H27KGC
Character Token Detector HA79V8
Christmas T7PVVN
Disguise 4DMK2R
Extra Hearts J9U6Z9
Fall Rescue ZEX7MV
Fast Dig Z9BFAD
Fast Magic FA3GQA
Gold Brick Detector 84QNQN
Hogwarts Crest Detector TTMC6D
Ice Rink F88VUW
Invincibility QQWC6B
Red Brick Detector 7AD7HE
Regenerate Hearts 89ML2W
Score x2 74YKR7
Score x4 J3WHNK
Score x6 XK9ANE
Score x8 HUFV2H
Score x10 H8X69Y
Silhouttes HZBVX7
Singing Mandrake BMEU6X
Stud Magnet 67FKWZ
Then, go get the one you'll be missing (#18) in the courtyard (with the pendulum... the area the ghost goes through a lot). Destroy the statues around the water and then build the pieces. Turn the red brick in to the bird toward the back.
Achievement unlocked!
EDIT: I did NOT need to actually collect any red bricks besides #18 to get the 100% achievement.