Hi Dave R & Filibis.
Changed the textures and removed the trees and the file went from 259 to 192MB.
As it was a model I built when I first started using SketchUp, I made some basic errors that's for sure following closer inspection. Some textures and model components were either too high for the resolution needed and too detailed for the final production. I think I was trying to include as much detail to provide quality to the model but in some areas was not required. Also, the terrain from the AutoCAD file was quite large and could easily have been reduced if I was building again.
Many thanks for your help on this.
