There is one requirement for the clothing you wear at an SCA event: that it is an attempt at pre-17th century clothing. And while "events" are dressed up, people usually wear modern clothing to weekly "practices".
With the focus of the SCA covering a wide range of years and cultures, this is reflected in the variety of clothing people wear. Some will choose to wear a simple belted tunic with baggy trousers, others will go to great efforts to achieve an authentic as possible appearance from head to toe. Generally, most of us are somewhere in the middle.
It is not necessary to be an experienced dress-maker or tailor to make clothing to wear to an SCA event. Like everything else in the SCA the goal is to learn through doing, and if you ask, you will be offered help.