OpenStudio and EnergyPlus doesn't support a true curve, but you can mimic a curve by using segments. This is in fact all SketchUp supports as well. When you make a circle (before you extrude it up) you can change the number of segments. Keep in mind, more segments means more surfaces within a zone. The radiant calculations at each timestep for a zone does calculations equal to the square of the number of surfaces. The moral, if 16 segments, or even 8 are fine, don't try 64.
What specifically are you trying to do with shading surfaces? Do you have a ring shading surface that matches the curve? If you used the basic overhang by projection factor you would end up with something looking more like a gear (with gaps). If you want a ring you could model it by hand. I would create a new shading group in SketchUp and then draw a segment circle equal to the size of the building. Then use the offset tool to create a ring. bigger by the desired amount. Then select the original circle and delete it leaving only the ring. Make sure you draw lines to segment the shading surface so it isn't non-convex, and so you don't have an impossible surface with a whole in it (EnergyPlus doesn't have surfaces with both inner and outer loops, in the situation of a window, if you look at the base surface in the data file, there is no hole, that is just how we represent it in SketchUp). If you are comfortable in SketchUp you could also just draw one segment and use the rotate tool to do a polar array to copy the segment around.
I attached images from a quick mockup.
Using offset tool
segmenting surface after removing inner circle from ring
