Question -  
How to create 3D Topo Surface (existing) ?  ..  by importing surveyor’s topographical contour plan.

Note:  Get your Surveyor to provide you with a set of ‘Contour Plan’ ..

1.  Open Surveyor’s Contour Plan in Autocad.

2.  Right Click =>  Click on ‘Autocad’, open ‘View’ toolbar.

3.  Click on ‘View -  Front’.

4.  Delete all entities in Surveyor’s Contour Plan except the Boundary & Contour Level.

5.  Scale up the imported Surveyor’s Contour Plan accordingly.

6.  Go to Format =>  Units, set value for ‘Insertion Scale’ to ‘Millimeters’.

7.  Launch Revit, open your Revit project and click on Site Plan.

8.  Click on Home =>  Link Cad, browse to your Surveyor’s Contour Plan and import as link ..

9.  In Revit, ‘Move’ the imported Surveyor’s Contour Plan into Site Plan using the boundary point as reference.

10.  Go to elevation view, using the highest contour point in the imported Surveyor’s Contour Plan .. ‘Move’ the imported Surveyor’s Contour Plan in the correct level using the level in revit’s model as reference.

11.  In Autocad, Open Surveyor’s Contour Plan and delete ‘boundary’ layer and all other layers, leaving ONLY the contour layer.

12.  In Revit, open the 3D view of the Site Plan.

13.  Click on Site menu =>  Toposurface

14.  On the Toposurface tab of the Design Bar, click ‘Use Imported’ =>  Import Instance.

15.  Select the imported 3D contour data.  The Add Points from Selected Layers dialogue displays ..

16.  Select the ‘contour’ layers to apply elevation points to, and click ‘OK’.

17.  On the Toposurface tab, click ‘Finish Surface’.

Toposurface generated based on the elevation points placed along the contour lines.