If you decide to make banana flour by yourself, it is very important to choose the right fruits. I do not know which all varieties of bananas can be used to produce the flour, but I have seen mostly everyone using only the plantains. They are quite large and ideal for cooking, as they tend to me more starchy and loaded with lots of healthy nutrients good for health. Just like avocados, if you want to increase your weight by using healthy food, adding plantains to your diet can help. It is generally believed that eating a ripe plantain everyday can improve your weight in a healthy way.
One cup of sliced raw plantains contain 181 Calories. Plantains are also a very good source of potassium and also many important vitamins and minerals including Vitamin B6.
Coming back to the topic, you can prepare really good quality banana flour at your home if you use good plantains.
Neither ripe nor very raw plantains are used, but the plantains that are close to ripening are used to make the flour. If you touch, the fruits will be little soft, but not mushy. And the colour of the peel will still be green, but starting to fade in to a pale green. The fruits at this stage will be quite sweet too. Once you prepare the flour, it will be mostly naturally sweet, so you don't have to add any additional sweeteners. However, the sweetness cannot be guaranteed, since some plantains take longer time to become ripe and sweet.
It looks like usual green bananas are also used by food manufacturers to produce the flour, even though I haven't seen anyone using them to make the flour at home.