Now in SolidWorks 2012, we can perform a swept flange and flatten it to capture the blank size. (Insert> sheet metal> Swept Flange)
Just like the normal swept feature, you need to have a profile and a path. Take note that the profile should not be a close profile. It should be open sketch.
Use flat pattern to unfold your swept flange into a blank size and save directly into .DXF for manufacturing purpose. Give a try.
Other popular links: