I've just started parkour and I haven't done any drops yet. But I have done rolls... from a standing position where the only forward momentum is from falling forward. I've been working on technique: what angle to fall, whether to roll diagonally, across, or along my body, how to face the direction I want when I get up, etc. This way whether I take a 3ft. or a 20ft. drop, I'll be better off 'cause I'm used to it. In "Jump Westminster" somebody does a roll on a parkbench. I couldn't do that yet. I'd roll right off the side 'cause I don't have the "body consciousness" or whatever you call it yet to be able to know where my body is and position and stuff without thinking about it. So point being, you can roll from any height (including no height), and IMHO I agree that beginners should start small and work up gradually over a long period of time. Patience will pay off.