Gluten free artisan/rustic flour mix

Does anyone have a mix with amounts for gluten-free rustic bread? My wife needs to avoid gluten and I’ve been hunting for a mix I can make rather than buy a pre-mix.

I have seen rice flour, buckwheat, sorghum, corn starch, tapioca flour, millet, vegetable fiber,
along with sugar and salt and xantham gum all used. I just don’t know the amounts and which of these are best to use. Any help is appreciated!

Thank you.