if i remember correctly, roasted barley is malted, then kilned to a toasty black. you can roast your own, but you have to get the oven temps just right and for the right time.
The simplest way to roast barley is in a coffee roaster. Trying to do it in an oven is very tricky. If roasted too much, you basically just have charcoal.
I wouldn't roast your own. For the lighter toasts it is fine but as David says there is a fine line between espresso beans and charcoal, Black Roasted and Charcoal as well.