In Revit, creating filled regions in a 3D view can enhance the visualization of your architectural design. Follow these steps to add filled regions in 3D view:

1. Open the Revit software and navigate to the 3D view where you want to add the filled region.

2. Select the 'Annotate' tab from the ribbon at the top of the screen.

3. Choose the 'Filled Region' tool from the 'Detail' panel in the 'Annotate' tab.

4. Click on the 3D view to place the filled region. You can use the sketch tools to draw the boundary of the filled region as per your design requirements.

5. Once you have drawn the boundary, click to finish the sketch and the filled region will be added to the 3D view.

6. You can modify the appearance of the filled region by changing its fill pattern, line weight, and color from the properties palette.

Adding filled regions in a 3D view allows you to visually represent different materials, finishes, or zones within your architectural design. This can help in communicating the design intent and creating more realistic visualizations for presentations and client discussions.

It is important to note that the filled regions added to the 3D view are view-specific and will not affect the model geometry. They are used for annotation and visualization purposes only.

In conclusion, adding filled regions in a 3D view using Revit is a simple yet effective way to enhance the visual representation of your architectural design. By following the steps outlined above, you can create filled regions to communicate different materials, finishes, or zones within your design and create compelling visualizations for your architectural projects.