In SU itself, you can go to "Components" and type "shed." This automatically search the Warehouse. It's not a great selection, but it does have a variety. John's suggestion is also very good. Using those search terms brings up some really useful models.

Well, of course you can do this in SketchUp - the only question remains the same however; if it is only for a 2D visualization, Google Maps and Google Earth itself would be pretty "enough". You can draw all inds of polygons there (with exact co-ordinates entered if needed), colour overlays etc. There could be some problems with imported terrain in SU if you are working in such a big scale (many acres). The ideal workflow is to import as little as ultimately necessary as SU has an orthogonal projection while GE has a spherical one and after a while (longer scale) the deviation between the two can be big already. But eventually you may also wish to see those buildings in 3D so for that, SU would indeed be needed (and a good tool).