How would you approach this? Lofting?

Attached is an image, it shows a work in progress of a layer of concrete I'm modelling on the finish structural concrete.

This new layer of concrete needs to be sloped in all directions to allow drainage to the gullies that you can see are raised above the structural slab. Where the joins are isn't teribly important, we just need to provide a solution but the final solution will eventually be decided by the contractor.

I'm do this by doing 2 sketches and a loft for each transition and it's very time consuming. I'm wondering - would learning how to model surfaces be beneficial for something like this? Eventually I need to be left with a solid so I can assign a hatch and section it later. Also a visual look around the building is required to check it will all drain without any ponding.

Image two shows all of the gullies (drains), they're showing as black as some of the edges need to be hidden, some are square and some are round. I need to do the whole floor.

well if you did a simple top sketch of everything you can go back and do a side view sketch and just draw a line, use this line to extrude a surface and you can then use this to slice or extrude/cut your solid. will there be a high point in the center of your slab or will it all run off in one direction?

in SW as long as you have a closed surface, its a solid(or can be).

Also, do you have access to floworks? it can model water.

try creating a surface then use it to cut the solid.