Depends on the cosplay.
For example: Someone like Carl Clover from Blazblue I will make myself with occasional help from Irene, while something like The 2nd Doctor I'll just collect the pieces from thrift stores.
When it comes to wigs, I get help from tas110 (Tommy, my broseph~) and when it comes to weapons I get help from either nora (Erin) or Blizzara Dragon (Clint).
I do a lot of commissioning for my friends as well (like you said, they buy the fabric, I sew it).
I think that goes with the topic of this thread.
(My apologies for horribly unorganized post, I'll modify it later >.>;