Help with lofting on a curved/ varied surface.

[amospettinger]

Hi.

I am trying to make lower curve (parts in yellow) to be a flat surface, and i want the loft to start from the "top" of the yellow parts (coloured in red) to the circle at the top. Both sides will need a different curve.

I have tried using the 3D sketch feature, but it didn't follow the base curve correctly, some guidance would be much appreciated!

I can share the file if needed.

[amospettinger]

Here's some more photos of my issue, "help2" is a top down view, the highlighted line is my attempt at the 3d sketch, but it is not consistent with the base, it needs to be directly above the outer base line, the inner base line is for the other wall. It needs to be a solid body. 

"Help3" is a side view, showing the curve if the item, the other side has a different curve, but they both meet.