Some of the kids at school asked about Google Sketchup -- so I finally made the time to build a quickie model and export it to Google Earth to see what it's look like.
First, I took a site plan and scanned it into a JPEG file. It's clean enough to see the building footprints. I had to guestimate the scale by drawing a line and scaling the line to a known measurement -- but not too tough:

Next, I found the Rivers School on Google Earth and exported a snapshot of that to Sketchup -- this is just a simple button click in Sketchup. It pulls in both a snapshot and the "terrain" (topography). It's kinda cool the way the shadows line up on the Google Earth image:

I could then match up the scanned site plan to the Google Earth snapshot quite easily -- boy things look so good when they're in Google Earth:

The model is very "blocky"; I guessed on all the vertical dimensions. This is more of a proof of concept.
The Sketchup .kmz file for the Rivers Site is here.