Is doing the conceptual designs on Sketchup and then making the workings/ Detail Drawings on Revit a good combination?

Of Course as sketchup is much easier & faster for making conceptual designs.

let me put it this way, you can use sketchup for mass modeling because it gives you more freedom and ease in modeling, and when it comes for importing into Revit, the mass files get treated as if they were made inside revit and you can stick your walls and roofs upon them and finish your documentation process, however, it would be better for you to check the mas modeling techniques because they can give way more powerful tools for modeling and using adaptive components in a way that can't be done when using imported masses.