SWEEP PROBLEM

Hi all, 

I am having trouble creating a square J-shaped structural fin. 

I first drew lines on where the beam starts, where it fillets and turns and meets the ground and extend horizontally. Divided the curves and created multiple "J"curves. 

Then I used the points to create a controllable rectangle, and tried to sweep the rectangle with the J curves as rail. but it just wouldn't do it.

Would anyone have any idea ? 
(the white shapes are done manually in rhino, just to get a sense of how I wanted to create the fins, but not generated from grasshopper)