Creating edge flanges with different shapes and angles

Ok, this is my first Sheet Metal part, and from the start it looks like it isn't using the basic features at all.

For some reason I just can't get it to work with Sheet Metal features only. I have a 3D wire frame that is fairly simple. There are some basic dimensions, but no dimensioned angles or lengths. This means I can't generate the edge flanges myself.

So to get some results, I drem it completly as a solid, and converted it to sheet metal. But I have to do some funky fixes and it still gives errors and strange cuts.

Can anybody point me out in how I have to design this thing the proper way?

SolidworksSheet Metal