Dress code is one of the secrets to a themed birthday party's success. Invite your guests to come in Harry Potter costume and dress like their favorite Harry Potter charcaters. If they prefer to go for a more typical Harry Potter costume, wearing the uniform of their own Hogwarts house is always a good choice.
A typical set of Hogwarts uniform includes a robe, a beanie, a scarf, a tie and a pair of gloves. Here we've short-listed where you can find the costume of your house.
If your guests are unsure which Hogwarts house they belong to, they can take the sorting quiz at Pottermore