If you know how to sew and if you know where to get the fabric, then one of the other key points is having the pattern or instructions to make what you want to make.
We find that places a lot of new members turn to first are the modern pattern makers. They often have Halloween patterns for the ‘medieval knight’ or ‘medieval princesses‘ that are inspired by historical (or Hollywood’s take on Historical) looks. The key point there is inspired by, they often miss the mark. Oddly enough for many of them, they make the garments more difficult to make than the originals were. Often taking more pieces, more seams and a more complex construction method to get to the end product.
Another instinct is to go with theatrical costumes. These stage costumes can also try to replicate the looks of the past, but are often made to be worn for short periods and aren’t as rugged and durable as the patterns we tend to use. They are made to ‘look’ right when on stage. They also tend to have alterations to make them easier to put on or take on back stage or adjustable to fit a wide range of actors’ body types.
The nice thing is that now more than ever before, patterns and help patterning garments is more available, online, for free. There are many blogs that go through step by step how to recreate various garments. There are websites that detail specific cultures and time periods. There are museums putting up images of the original surviving garments online. There are tutorial videos that lead you step by step through the process. And there are many events and classes held in the SCA where help can be obtained to recreate various garments from history easier than you imagined.
Stop by your local meeting, where dressing up in historical clothing is optional, or ask on line and members of the SCA will help you with your questions about historic costume patterning.