I think that if you begin with a solid curriculum of reading and invest a little bit of time in educating yourself about this, then the whole process will move much more smoothly, with less worries or mistakes, and with more confidence and success. So I suggest 3 things, in chronological order:
Zero step: Don't listen to me. Think for yourself! Think critically of these suggestions:
First step: I know that many of us don't like to immediately spend money on information, but it really is helpful to buy the book available at
http://www.rocketstoves.com/ ($15 for an eBook (immediate download to your computer), $23 for paper-back ) --- or else try to borrow a copy of the book from a friend or library. The book is very informative and should help to cool any stress; just be patient and read it thoroughly and patiently, slowly (it's a short read anyway).
Second step: Now that the first step gave you a solid knowledge-base on Rocket-Mass-Heater-Technology in general... Consider reading, from start to finish, the portable-rocket-mass-heater thread on these forums (
https://permies.com/t/2558/stoves/portable-rocket-mass-heater) or the original rocket-stove-butt-warmer thread (
https://permies.com/t/1078/stoves/rocket-stove-butt-warmer). These threads will give you a 'discursive' education about the subject: you will get to read about a lot of new ideas and questions, as well as the responses and critiques of those ideas and questions; rather than forming your learning about RMH's in a fragile straight line, you will learn by wandering and circling through a variety of information. This will fill-out your understanding, providing you with critical flexibility, the strength to improvise and think for yourself.
Third step: Now that you have a crazy awesome knowledge base, you're ready to think critically about the media: Watch all the videos at
http://www.richsoil.com/rocket-stove-mass-heater.jsp . Listen to the podcast at
http://www.richsoil.com/permaculture/182-rocket-mass-heaters-permaculture-podcast-019/ .
Fourth, bonus step: Return to these forums, ask crazy awesome questions and respond to more people's posts. You may certainly do this along your journey, You do NOT need to quaratine yourself away from the forums until you've completed this curriculum-- hell, I have NOT completed this curriculum. I wish you success though!
Again, taking a few days to educate yourself thoroughly will make the whole process of planning and building progress much more smoothly.