I don't know what you mean by oat flakes...

Like potato flakes that should be made completely creamy with water?
Anyway, what I do is to buy the quick-cooking oats ("Cooks in 1 minute!" according to the box

). If I'm just doing oatmeal, I do a ratio of 2 parts oats to 3 parts milk (e.g. 1/2 cup oats to 3/4 cup milk). Stir. Microwave for 90 seconds (for the 1/2 cup oats size). Sweeten. Eat.

I use milk because it seems to make a creamier consistency than water.
If I'm adding applesauce for ds, the ratio is more like 1:2:1 (oats:milk:applesauce), although I've never officially measured it. I don't make as much at a time for him, so the microwave time is less.
I've never cooked it on top of the stove

, so if you don't have a microwave, this doesn't help you at all. Sorry... I really do hope something in that helps some...