Hi Dan
I am not entirely sure I understand what it is you are trying to do OR what you are asking.
That is .. I have NO Idea what a "Grass Market" is OR a "uni project" BUT if all you are trying to do is Download a model into SU (SketchUp), then Click on the Model in GE (Google Earth) or click on it's image that shows up in the Balloon in GE when you click on the model, then on the Model's Info page, select DOWNLOAD (top right corner of the model info page ... Big Red Button).
If the model is not being shared, that is ... it is not available for downloading, then you might have to create your own model ... which will often result in a better model anyway.
As you can learn from MANY Video Tutorials, it is not difficult to create your own model(s) and they can be created by using different available methods.
One way is to download the Terrain Data from GE into SU which will help you Geo-Locate it as well as giving you a Top Down View enabling you to model to the correct Scale. Once you have finished modeling (to whatever level of detail you like), you can either use any of SU's Textures/Materials And/Or using your own Photos/Photo Textures.
Another method is to use the Match Photo feature in SU which allows you to Import Photos and model to scale directly from those Perspective Photos.
You can use your own models any way you want, however, Google no longer accepts models for use in Google Earth.
I hope this information helps you achieve whatever it is you are really trying to do.
Happy Modeling (if that's what it boils down to !!).