Since sheet metal walls attach to edges and creating a wall removes the original edge and creates a new one, you really cannot pattern them as the primary reference is eliminated. Creating a single wall all the way around and creating a cut that you then pattern is the way to go.
However - you still won't be able to flatten it due to the curved bend line. The sheet metal module was made to simulate press brake kind of features and doesn't do well with complex metal forming.
I got a tip to try to model the cyl as a polygon and put one tab on each (straight) segment of the polygon. This would more accurately match what happens in the shop in fabrication. But, modeling that is a bit more complex for sure, a basic exercise in relations and polar geometry.
This is (supposed to be) a quick and dirty one shot deal to do some testing on the floor. This is not a released part for mfg. Isn't it always the case ? The seemingly simple turns into a complex nightmare.
No - I take it back; I am not whining. Things have been much worse. This would actually be fun were it not for those confounded deadlines.
Typical pro/e workaround.. you have modeled the round part, you could determine what the flat length is off of that, then model the whole thing in the flat. In the end it's a one off and you just need a flat pattern.
Unbending those curved bends would involve deform features (I have little experience here) and would take a long time for little return. I say fake it and just model it flat.