So I made my own Hogwarts bunting for my party.
I have uploaded my lettering which you can print and cut out in order to make your own!
You can access it HERE from dropbox.
The sizing for the letting is all correct if you use A5 paper or card as your background.
Gryffindor - Yellow letters, red background
Hufflepuff - Black letters, yellow background
Slytherin - Grey letters, green background
Ravenclaw - Grey letters, blue background
I used approximately 200-220cm of string per house - 220cm for Gryffindor and Hufflepuff (10 letters) and 200cm for Slytherin and Ravenclaw (9 letters). I had 15cm at either end in order to hang them and about 3-4cm between each "flag".