Funny you posted this because I did the exact same thing on Friday night...got bored, went downtown and took some pics. Wasn't so luck with the rooftop shots though.
My plan was to go to the rooftop of some of the parking ramps. Hadn't planned on the fact that most are gated (real gates, not just the little arm). Oh well...
Found a...for lack of a better word...cobblestone road (brick pavers, etc) with a brick apartment building on either side. The way the light hits it makes it really cool for an HDR image. Failed with the composition, so I'll try to get it again this weekend if the weather is cooperating.