Hi RodrigoMW,
It’s a normal design process but enhanced with UE. It starts with sketching on paper, just testing ideas. Once I think I have something that could be great, I start modeling simple volumes and spaces in SketchUp - just the key elements. If it still looks promising in SketchUp, I test the design exporting it to UE. In UE I do a low/medium quality lighting calculation and evaluate (walk around) the design. At that point, it’s either refining that design or starting from scratch and adding new designs as new levels to the UE project. That way, you can always go back - or show the client the alternatives if needed.
Light and space are very important to me and UE to me is a tool to test those qualities in a design (SketchUp’s shading capabilities are very limited so there’s no feeling of depth). I don’t think using UE changes the design itself - it’s a tool that helps me evaluating the design myself. Also, it helps communicating the design(s) in the end. Clients really get a good ‘picture’ of what the design is about and how it could look like. Anything that helps my clients making a decision might save time and streamlines the process.