You can't substitute a recipe with just one type of gluten free flour. Especially with bread baking. Some gluten free flours are more denser than others and the outcome of using just one will be disastrous.
For lighter, fluffier bread, the flour blend with be mostly starches but the nutritional value will be very low. For a denser more whole grain bread, the flour blend will be mostly a mix of whole grain flours but the outcome of your bread tends to be gummy.
The following will give you a guideline to produce different types of bread depending on the amounts of flour types. And remember the percentages are by weight, not volume.
Light-textured bread with a "white wheat flour" feel:
50% starch, 50% lighter whole grains (grains that are lighter in color tend to have a milder flavor)
Dense, whole-grain bread with deeper flavor, try:
30% starch 70% whole grains
Sandwich bread with flavour, texture and stability:
40% starch 60% mixed whole grains
Personal myself I prefer the 40/60% blend.
Next is what flours to use and how many. Understanding the different properties of each flour will help you pick the right product for the job. They can be divided into three ‘denseness’ categories: light, medium, and heavy. Remember that I'm talking about the lightness or heaviness of the flour, not the flavor.
Lightweight gluten free flours, or the least dense, are your starchiest flours and are generally neutral in taste. Arrowroot, cornstarch, potato starch, sweet rice flour, tapioca flour, and white rice flour fall in this category. They're technically not flours at all but used as such to enhance the quality of gluten free baked goods.
Mediumweight gluten free flours are, on average, more nutritious than lightweight flours. These flours have a little more body and bulk, including amaranth, coconut, garbanzo bean, millet, quinoa, sorghum, superfine brown rice, and teff.
Heavyweight flours are going to produce a much denser final product. These flours would also be more nutritious than starchier flours. Nut flours are obviously higher in fat but are packed with omega-3 fatty acids and other good-for-you nutrients. Almond flour, regular brown rice, buckwheat, stone ground cornmeal, and any other nut meal (walnut, pecan, chestnut, etc.) would be considered heavyweight flours.
Try using at least two starches and two to three whole grains in your blend. I recommend using an equal portion of potato starch and tapioca starch. Potato starch seems to absorb too much water while tapioca flour doesn't absorb enough. Exactly equal portions seems to be the best blend for these two flours; they compliment each other well at this ratio.
Here's a suggestion on how to blend flours for a recipe that calls for 450g flour:
100g sorghum flour
100g millet flour
100g buckwheat flour
75g potato starch
75g tapioca starch
(Also, remember this: if you want to convert your favorite gluten recipe gluten-free? Start by subbing 140 grams of your flour mix for every 1 cup of gluten AP flour.)
So get out there and see what sort of flours you can get in your town and start blending!