Here are some pictures illustrating my workflow when creating environment. I always start from paper, drawing some ideas, before starting any 3d. Then doing a line-up helps me see the building next to its neighbours to make sure that it fits in. Once I'm happy with the design, only then I start modeling in Maya and do the texture in Photoshop, with the help of other softwares like Mudbox or Quixel Suite when I need to add details. I usually test the building in a neutral lighting scene and in the environment it's going to be in.