You think about how big the circles should be on the sides.Maybe you take a cup or a glass as a template.From this you make the two side parts.The length of the fabric is now calculated as described here:
Small round handbag on the belt of eco-leather. Comfortable, small and quite roomy. Fastens with a zipper. It is put on a belt, hands at the same time remain free. The diameter of the finished bag 14 cm.
Initially, you need to choose the material from which the Fabric will be made to be natural: cotton or linen. The fabric of synthetic fibers is not suitable, because it melts from high temperature.
The filler should not pass heat and not melt. I will use cotton batting (but now there are imported heat-resistant fillers on sale).