I used Butterick B4861 and this amazing tutorial to help me make sense of the fly. Best tutorial going!
They are made of cotton drill scraps I had in my stash and a lilac zip because that was what I had to hand.
Still, I like them and I am thinking about using the pattern to run up some trousers, if only because once again Katrin has ruined hers... I have no idea how I'm so hard on her clothes!