My dad really likes the America's Test Kitchen How Can It Be Gluten Free Cookbook, mostly because of one thing: non-fat powdered milk. Including this in a flour mix helps the bread's structure, and also helps it brown, giving it a more traditional appearance.
We call this the ATK mix, even though they only use rice flour.
2 cups brown rice flour
1/2 cup buckwheat flour
1/4 cup white bean flour
1/2 cup tapioca flour
1/2 cup potato starch
1-1/2 tablespoon nonfat milk powder
This gives just under four cups. If you need four cups for a recipe, just add more rice flour. We keep a container labeled ATK, because a lot of baking recipes just use 3 cups, and the extra then goes into storage.
This mix is used in our coffee cake recipe.