All is dependant on what you want and the size of your project.
However, a or b or a&b in combination are the "standard" way of seperating your files.
In most cases I try to keep "links" in a seperate model for several reasons.
The most important is keeping your main model as "light" as possible, and also with less other things linked in less chance of corruption.
Also this way people arent loading in dwgs and forgetting to tick "only the active view" - having all your links in a seperate model allows you a bit more control graphically, and seperates other risks from your main model while keeping the file size down.

These days, depending on workflow, I would have a seperate file for the topo, because I have other workflows that involve civil 3D and dynamo and this allows me complete isolation when I work on the topo surface and stratas and then the landscaping for construction... so a "links" file containing dwgs and another seperate file for the topo.

Also triangulation is generally better than creating your surface from contour lines if you have it available.

I used to do separate site/model files, each with shared coordinates and linked together. However the workflow got to be just too much of a pain since we often jump around between the site and the building modeling. For a large site with multiple buildings, I would probably still do it this way. But for a small site with a single building, I now keep it in the same model.

To get the building up at the correct elevation, and also have the toposurface points read the proper elevations, I now use a method posted by user jeffh on AUGI some years ago:

Eh? If the Z-heights in your .csv are correct (to the units you are working in your project) and your SBP is at 0, the topo. tool works as it should without having to do any of that.

the elevation of the points imported will be relative to the level you link them in - so if I place a Survey file at level 2 (+8m) then my points when I create topo surface from linked cad file will be created 8m above where they should and I will have to relocate the topo surface after I create it. Like all revit elements it is created relative to the plane of reference it is associated with.

If I use the method of making a level 0 (Sea level) and then create "project" levels up at +436m for example then as long as I link my cad file in on level 0 (sea level = 0m) then my topo will place correctly but I will have a level 0 that is entirely useless for my project. This can cause other issues with massive zoom extents and things like temp dimensions wanting to snap to the 0 sea level. I often create another level type for sea level so I can mask it in my view templates.

CSV files are a bit different in that it will automatically "find" 0 or points will be created from 0 sea level and technically should be at the correct level relative to sea level.

Karalon10,

Yes, my .csv file creates a toposurface some 200 m above sea level. I would like to keep it at it’s correct elevation if I can but more importantly I need my levels to reference a 100 m datum at the top of the main floor? Is there a way to do this? Thanks for your previous response.

**Update**

I figured it out...

Build your model relative to the Topography at it’s naturally occurring elevation.
Unclip and drop your project base point 100 m from the top of your main floor.
Edit your level type to reference the Project Base Point.

If your toposurface is a link you can conveniently clip and move your Project Base Point (and the entire project) relative to the toposurface if an elevation change is needed.

If anyone sees a problem with this method please advise. Thanks!