In Revit 2012, you can create a selection and isolate, hide, or apply graphic settings for the elements in the selection. You can also load the selection later to make the elements selected again, and set the "Comment" parameter, or copy/paste aligned to other levels, etc.
Here is an example:
1. Select the beams, columns, and floors on the second floor plan.
2. Click Manage tab > Selection panel > Save.
3. In the Save Selection dialog, enter the name "2nd Floor structure".
4. Click View tab > Graphics panel > Visibility/Graphics.
5. In the Visibility/Graphics dialog, under the Filters tab, click Add.
6. In Add Filters dialog, select "2nd Floor structure", and click OK.
7. Set Lines and Patterns under Projection/Surface, and click OK.
You will see the beams, columns, and floors display using the defined line color, weight, etc.
8. Click Manage tab > Selection panel > Load.
9. In the Retrieve Filters dialog, select "2nd Floor structure".
You will see the beams, columns, and floors on the second floor plan are selected at once.
10. In the Properties palette, set the parameter "Comment" value as "2nd Structure".
11. Click Modify | Multi-Select tab > Clipboard panel > Paste > Aligned to Selected levels, select Level 3, and click OK.
You will see that all the beams, columns, and floors on Level 2 are copied to Level 3.
12. Open a 3D view, follow steps 8 and 9, and click "Isolate Element" in the view control bar. Then only the second floor structure elements are shown in the 3D view, and you can export your second floor structure to DWG.
TIP: In step 10 (set the parameter "Comment" value), you might use it as a Find Item criterion after exporting a Revit model to Navisworks.