You have a couple of options really.
There are several different components to the model and different texture groups.
For instance a metal roof is going to have a higher specular level than say a trash bag/ wooden fence.
I would suggest that you uv map individual parts of the scene and then texture each part separately.
you could try and go the long way round and try and paint in a model painter
Finally you could go crazy and try and auto uv the whole lot and work out what part is what and texture it all on one image lol
Peace
