Sheetmetal - Blend -> Sheetmetal

I have a part I am trying to make in sheet metal. I haven't done a lot of sheet metal so I am asking for some starting tips. I have a one part that I started with blend and am trying to convert it to sheetmetal. Should I do that before the raduii are applied or after. It is coming up with an error when I am trying to choose the driving surface. I think the part constant thickness (which is what sheetmetal needs).

Thanks, Dale

Here is the other discussion where I started in sheetmetal:

http://communities.ptc.com/thread/57370