I have played around a bit more with Mission Architect in the open beta now and have created my first story arc.
It is called The Siren Supremes and is a 3 mission arc. There is certainly more work that can be done to it, but it should be at least good enough to let others try it.
It was not so long ago I started to think what missions I might want to create. A thought was to create something around some of my villain and hero characters. The first guineapig here was a character called Shadow Siren.
Before I had a look at Mission Architect I had some vague ideas of the settings I wanted to do. Those I had to scratch; the maps I had been thinking of were not available and I did not have the mob placement control that I had hoped for.
So new ideas had to be made and the story formed and changed as I played with the tools.
First mission has level range 5-40, the other two 35-40.
Edited: I have done a few changes back and forth with maps and difficulty settings on some mobs. Especially the final part was a bit too easy initially.