Can I make a gluten free sourdough bread?
I’m generally using millet (a gluten-free grain) flour for sourdough starters for various fermentation applications. Simply my starter recipe for millet sourdough is as follows:

Mix 50 g of millet flour and 50 ml water in a very clean glass cup. Cover the glass using a piece of paper towel or cheesecloth. Give it some time to ferment for 1-2 days (or until you see get a bubbly texture in the  mixture) at room temperature. 
You can directly use this as your sourdough starter.

In order to get your dough to rise, you need to use some thickeners to replace the gluten. One of the most popular choices is using Xhantan Gum, but Locust Bean Gum is sometimes used as well.