I built what I could before I needed to cut more struts.
The best advice I can give is to make the first course of triangles fit as tight as possible. Any errors at the bottom become bigger errors as you go higher. I am considering tearing the whole thing down and fitting everything closer. We'll see.
Here I have loaded several struts onto my saw table with a temporary stopper. I set my radial saw bevel at 12.5 degrees and used it to cut the first of many angles on each end.
Again, painting each length makes life a lot easier.