Research costume and dress specific to your selected African region. Africa is a diverse continent, and the native dress of its citizens will vary from region to region. Resist the urge to classify "Africa" as one homogeneous entity, and research your specific African nation to respectfully and accurately begin your designs.
Source materials that will complement the designs of your chosen African region. Kente cloth is an instantly recognizable fabric, made of intricately woven strips that have been sewn together to form a large bolt of material. Aso oke, Adire, Kitenge, Mudcloth, Barkcloth and Kanga are other common African fabrics, many of which can be purchased online. Each originates in particular regions of Africa, and the colors and motifs used in each piece come with specific meanings. Be careful to use materials and patterns indigenous to the region you are representing.
Choose patterns that are loose-fitting and simply constructed. In general, African costumes are made of simple tunics, pants, dresses and head wraps in bright and earthy colors. Companies such as Dupsies, an online African clothing store, offer traditional African garments and include many images that can serve as a starting point for your pattern search.