Daniel -
This part is going to be difficult to model as "sheet metal" in
SolidWorks. You can approximate the transition using a lofted bend
and create a 3 piece assembly with the round drain and the box with
flanges at the top. (Lofted bends don't play well with edge flanges
and miter flanges.
If you just need a representative model (won't unfold) then you
could do something like the attached.
This part is going to be difficult to model as "sheet metal" in SolidWorks. You can approximate the transition using a lofted bend and create a 3 piece assembly with the round drain and the box with flanges at the top. (Lofted bends don't play well with edge flanges and miter flanges.
If you just need a representative model (won't unfold) then you could do something like the attached.