This was a hard one to do, you really have to think about what you are going to model when the tri count is so low. In my case it was especially challenging because my building was mostly round, which of course uses lots of polys.
I decided to model a Canadian Landmark, the Montreal Olympic Stadium. See below for the picture.
I started off with a sphere, scaled it up properly, then added the dimples for the roof mat. I also removed a large part of the top and bottom to save on polys.
The arch section was just a box with taper and bend modifiers applied. And I used simple splines for the wires. That's about it.
