A reader reminded me that I needed to discuss this:
When I assembled my struts, it involved a lot of muscle and an imperfect fit. I knew that a 3V design would leave an uneven base, that is the first course would not sit perfectly on the base wall. As it turned out, it wasn't a huge deal, but everything would have fit together better had I know about the Kruschke method.
Instead of 3 strut lengths, there are 4. The resulting structure gives a flat base to mount. For a little extra measuring, you will save a huge amount of aggravation and you will be happier with the end product, especially if you like things to fit perfectly. Check out Domerama (link above) for the calculator and assembly diagram.