The main ingredients to make gluten free bread are flour (rice flour, corn starch, Cassava, defatted soy flour, quinoa, and chickpea flour), xanthan gum, and others materials that used in noraml bread.
The main starch source is usually rice or corn. Current trends show that new crops commonly called "ancient crops" such as sorghum, amaranth, quinoa, teff and millets are coming into picture as they have many health benefits. There is also a growing trend of having multigrain gluten free alternatives that contains flour to grits or pieces of 5 to 15 different types of grains including beans, nuts and cereals. I hope this helps