Attempts to create a 3D view of a Legionary Fortress

I have spent many HOURS messing about with a free version of Sketch-up, trying to create some features of Legionary fortresses. Here are some 2D stills from my attempts. I do find it useful to attempt this as a 3-d tour around these buildings gives you a totally different perspective.

View from outside Main Gates

Overview of Principia building

View from inside main gate up the Via Praetoria, showing a Granary to the left and the Principia in the distance

View inside Principia building, towards the Legionary Shrine.

Plan view showing principal gates, streets and zones.

I think the speed of my laptop has made this harder than it should be as it always seems to lag behind mouse clicks and so things keep going wrong (I know a bad workman..)