Hi
I had a misunderstanding considering the challenge, and I think I am not the only one.
After the Lecture about Extruding, the challenge is to make a Mayan Pyramid. The majority of us probably thought they had to make a finished Pyramide, with stairs and everything… Somehow we succeeded and went to the next lecture, just to hear “now we are gonna see how to make the stairs” 
I wanted to cry 
I had created the pyramid and then the stairs, and merged them. It was not really a waste of time, I learned a lot, but I will redo the pyramid.
The course is great, by the way 