Slabs are easy.
With the polygon editing palette, irregular slabs are easy.
For complex section geometry such as a corrugated sheet, you need an object. But such an object is usually rectangular. There is no polygon editing for object elements. It is difficult to code even pseudo-polygon editing into an object, and still the palette wouldn't be available. More to the point, AC library objects such as corrugated sheets certainly do not have this ability.
So place a slab and the object. Make the object extensive enough to cover the whole slab. Put the slab on an SEO operator layer. Perform an Intersection
solid operation with the object as target and slab as operator.
Then you have this.
Then you can edit the slab like a slab.
And the intersection is updated.