I would start with the ground up and keep thin outside lining when doing the trees :)
It depends on what you are talking about when you say "create the look".
Most likely, the answer you are looking for is the Director, because the Director will give input to the costume designer on the character's look and how it fits into the overall design elements of the entire production.
If, on the other hand, the question is asking about who assists in building the costumes, then the answer is the Wardrobe assistant.
Again, it all boils down to if "create" means design or construction. In context, my best guess is it's referring to design, in which case the answer is the Director.
Using all of it at times and only small parts of it at others..... not fully certain
