Mike, with the ones where you are fitting the bottoms of two pop cans together, that is the hardest part of the build.
The first photon stove I got to fit together took me about 20 cans.
When they tell you to save a full can to swage the one can bottom open a bit more before trying to assemble them it is good advice.

Here is a site more dedicated to backpacking stoveheads.
http://www.bplite.com/index.php