LEGO Harry Potter Collection

You will need to have earned 5 Gold blocks first.

Once you have 5 Gold bricks, quit to The Leaky Cauldron and make your way to Diagon Alley, head to the end of the alley (Far right) to Gringotats Bank once inside construct the first vault door using your magic, then open the lock using the character with the key.

You'll find a small green block inside, walk up to it and press , the only option you'll have available is to Play Bonus Level accept this and do the task (Should be to gather 100,000studs for the Gold brick) Once you have finished you'll be brought back to the bank.
This time when you walk up to the green block you'll have 3 options, the only one you are interested in is the bottom one which is the building tutorials, do all 4 and the achievement is yours.