Hmmmm............. I hardlly no where to start..
Here is some things I can think of. Central boiler builds a good stove. However, a lot of there designs are extremely hard to copy and there are other ways of achieving the same or BETTER efficiency than going with that ripple roof. SOMETHING TO CONSIDER: The more welds you have on your firebox, the more likely you are to have problems. If you have a ripple firebox and then have it square, you are going to have like 20 times more chance for a leak than going with a round firebox. You may say or ask how do I achieve the efficiency, well first of all look past the hype of central boiler. As I said they are good stoves, but dont get hung up on their ideas.
Simpler ways to achieve more efficiency is by having a drop chimney in the stove, instead of it being in the top or the back, the chimney will enter from the top at the back of the stove and extend down to within 6" of the bottom of the firebox. This keeps the heat from being going straight up and out the stack and aids in trapping gases in the top of the stove giving it more time to extract heat and a better chance to burn the gases. Some models even have the water jacket extending on down into the firebox surrounding the pipe, natues comfort would be an example of this. Another thing you could do is make a double pass. When building your stove you could have the exhaust travel inside your water jacket through a jacket/pipe from the back of the firebox, to the front, and then back to the back. Triple pass or Double, whichever, it simply allows for more time to burn and cools the exhaust which means MORE EFFICIENCY.
Now, as far as natural draft vs forced. It has been proven in test that having a fan is more efficient. By having the fan you are forcing o2 into the fire which makes the stove recover faster. Also, when there is enough air being forced into the stove it increases efficiency by allowing a more complete burn of your wood. Think of a torch and how lazy it acts until you shoot the o2 to it then it comes to life. Same thing happens when burnign wood, a roaring hot fire is wasting less than one sitting there using a natural draft and puffing away.