First of all, I was quite overwhelmed by all the lovely comments I got on the yellow hoodie! Thank you so much! Besides that I also got questions about how I made this hoodie. I did not take enough pictures during the making for a complete how-to, but here's some more about the process.
As I said, the horizontal seam was inspired by my niece Marie's coat. I emailed her a bit late though, so when she sent me her drawing with measures I had already started to improvise. Marie's coat has a very big hood, I made mine somewhat smaller.
My design differs from Marie's drawing, but it helped me understand how a horizontal seam works. The height of the bottom hood-part is important because if it's too low, the hood will not hold itself right. It's also crucial to make a muslin of the hood before cutting your fabric, for this will show how your hood will drape on your head. It took me several hours to get this right! It was a long process, in which I adjusted my paper patterns four times in total. Below you can see the difference in the second and the last version. The triangle piece is cut twice, the other parts once.
Below shows the way the parts fit together. There was no need for any fusible interlining, this fabric is quite sturdy. But if yours is not, I'd use it in the rim to give it some shape.
UPDATE: Get the measurements to draw your own pattern HERE!