Every Fall, my mom and I take a girls trip to Orlando and make an obligatory stop at Universal's Wizarding World of Harry Potter. And every year, I threaten to make and wear some wizard robes (for both of us). And this year, I finally got around to it.
[Update, 2018: I've now made 4 sets of robes: one for each house.]
I started with a quick google and found some patterning instructions.
But there were a lot of measurements missing from that pattern so I had to fill in a fair few blanks on my own. And do some tweaking once the robes actually went together. (Luckily, I made two sets of robes so I was able to fiddle around with the second set and work stuff out.)
Next up: finding the right fabric. I made a Madam Hooch costume a few years back and it was black crepe back satin (I used the non-shiny side) and lined with dupioni silk, which gave it a nice structure. That was my intention again except that apparently JoAnn Fabrics doesn't carry silk anymore. Luckily I did find a nice Casa Collection matte satin in almost exactly the right Gryffindor Red (and one in Hufflepuff yellow for mom).
I used the less shiny side even though it was technically a matte satin.
Once the pattern was made and the robes cut, they went together amazingly fast. I just serged them and didn't bother with any actual sewing....except for sewing on the house crest patches and putting the sleeves in.
The patches were a whole other quest. I was going to use the ones they sell at universal. They fancy.
But the robes universal sells use a simpler looking crest. And so I decided to use that instead. I found a Gryffindor one on ebay. Easy.
But poor beleaguered Hufflepuff...I couldn't find one for them that didn't look like it had won sixth place in a you-tried competition. (I'm not naming names, but give it an Etsy search and you'll see what I mean.)
The one I ended up buying, when it arrived, was a bit smaller than I would have liked but at least it is definitely a badger.
[The Slytherin and Ravenclaw crests also came from ebay.]
At any rate, here's the pattern as it ended up. It's sized for me at 5'5". I used 4.5 yards each of the black crepe back satin and the casa collection matte satin for the lining (bordeaux for Gryffindor, ochre for Hufflepuff, eventide for Ravenclaw, botanical for Slytherin. (Don't but them full price--get your hands on a JoAnn coupon...there's always a coupon.)
So now you can make your own and we can all go enjoy a butterbeer together!