My easiest and most precise method isn't to roast the flour, but to "fry the flour" instead. This method provides much better control and ensures the roux is precisely as dark as you like.
--- Put one cup of flour in a non-stick pan.
--- Turn the heat high as if you were using the conventional method.
--- Using a non-stick spatula, continue to keep turning the flour.
Within a minute or so, it will start to smelling like popcorn. Watch it with a bright light, and you will see it turn very light brown. The flour will also start to clump a little.
--- "Fry" for about 5 minutes or so, until evenly as light brown as you'd like.
--- Turn heat off or down
--- Add a stick of butter, and finish the roux without adding any more heat.
You will notice that once you add butter, it immediately becomes much darker than you thought it would. The oil in the pan to conducts heat much better, and it now will cook extremely fast, so make sure that the heat is not too high.
If I'm using the roux right then, I start adding my liquid after the butter is mixed in.
I've found that I can control the heat perfectly this way and it won't be over or under cooked. Using the standard method with my electric stove either over or under cooks it. The only way to cool it fast enough when too hot is to put it on granite, which is not the best.
Thanks for validating this method @Barry, (and helping me discover that my method was not unique ).
-- How does the gluten in my bread flour affect it?
-- If you use another oil, do you need add liquid to make sure it thickens, or just wait until you use it in a sauce later?