this seems like such a simple thing...

I have created a new part in an assy. Simple sweep from a 3d sketch.  I want to create another but the plane for this one will be offset from the plane (used a face, not an actual plane) of first.   I'd like to just do this on the fly - choose the first face then put in offset dim, but all it asks for is the plane and no other option.  I was used to ProE (maybe a plus of Pro over SW??) where you always had an option to "make datum" whenever you wanted to place pretty much anything.

Do I have to create an actual plane for this next one?

thanks again,

Bonnie