Photo retouches are a great visual when the main building is existing and changes are made to a portion of it.
New entrances, additions, color changes, roof changes, (or whatever your change) are rendered onto the photo of the existing building. Either my client provides the hi res photo file or i can shoot the photo (at an additional charge) of exactly the view to be shown. I then get a large hi res photo printed and i render the changes onto it based on the plans or notes provided. The final image is photorealistic, showing exactly how the project will look when completed.