Good Morning!
What specifically are you trying to create in sheet metal? I ran into a huge problem designing ribs for an all-metal airplane when I tried to start off with the sheet metal feature.
I ended up using surface offsets to find the flat pattern without my flanges, then drawing out the entire sheet metal pattern by offsetting the curved edges from the flange-less flat pattern out the distance of their intended width.
Whew. I hope that last paragraph was coherent...