I've done more than 50 shirt designs over the past 7-8 years, and I really have enjoyed designing these.
I'll ask a few basic questions and get any files needed from the client. I will then create 3 or more different shirt designs (unless the client has something very specific in mind in which case I may create a few that are very similar). I can send the shirts in to be printed, and all the client will have to do is pick them up and pay for the printing costs. Or I can give the client the design in EPS and they may take care of printing.