There is actually a lot of stuff available to aid in your costume design. Books, artwork, movies, web-sites, commercial patterns, other performers and costumers abound. Books are plentiful especially since Renaissance faires have gained popularity. Below are my favorites. Most of these books can be found through your local library or for sale.

Costuming References

Janet Arnold, Patterns of Fashion; 1560-1620: Arnold is the grand dame of historical costuming. She's drafted patterns from original garments. You do need experience to size the patterns for the modern body but you'll have a pretty authentic outfit.

Hill & Bucknell, Evolution of Fashion, 1066-1930: This book shows how fashion evolved. I found more useful the discussion on how the styles affected how the wearer moved and what posturing developed to show off the clothes.

Jean Hunnisett, Period Costume for Stage and Screen: Period Costume is also for the experienced sewer. The clothes are designed for theatrical settings where they'll get rough usage but need to be visible to an audience and convey a story.

Roy Strong, The English Icon: Strong has collected hundreds of portraits of English nobility during the Tudor, Elizabethan, and Stuart reigns. This is a great resource for upper-class costumes.

Janet Winter, Elizabethan Costuming: This is a great starter book for building a faire costume. It is for "Renaissance" costumes as compared to reproduction clothing. It covers men, women, and kids clothes for all stations, has basic patterns, and talks about accessories like hats, shoes, and pouches.