I'm no expert, but if you want to stick with that background picture you need to change your camera angle and view cone i.e. make the camera height and target height more similar to correct the vertical perspective. Also, you may have difficulty with lighting, as it appears from the background photo that the sun is behind the camera, judging from shadow directions. Hard to make your building interior look good if you change the angle of your modelled sun to match, although I'm sure Dwight would have a way of doing it 
