After I find the good angle, then I start looking for the sky for environment. You can find nice and good sky environment here http://vyonyx.com/2008/09/15/references-backgrounds-vol2/.
By click ALT+B in view camera, select the place that you save the image and click display background. After you did, put your same image in environment, and material slot. Now the sky can show in your perspective. You can match and know where the good cloud environment that matches with your building is. In this stage, I use vray sun, so I can get some shadow and depth from building. This is vray sun setting that I use for it.
After making the environment, I begin the texturing with unwarp method.