I have posted in the past on how to create interior elevations/sections by only using Photoshop, but I never posted on exterior elevations. The workflow that I use for exterior elevations really isn't much different than the workflow that I use for interior elevations. The only change is with the shadows. In my interior elevations tutorial, I gave depth to the illustration by selecting certain surfaces and painting in shadows and highlights. However, with exterior elevations, I streamline the process by exporting a shadows layer from Sketchup. With this shadows layer, there is a key move that I use which quickly and easily gives depth and clarity by utilizing the Burn tool. While I don't go into a great amount of detail in this post, the process of using the burn tool is more thoroughly explained in my "Ambient Occlusion" video tutorial. I would also suggest taking a second look at my "Interior Elevations" tutorial since the overall workflow of that video is similar to what I used for the above exterior elevations.
1. I began by exporting 3 images from my Sketchup Model: 1) Just the line work with the shadows turned off and the face style set to "Hidden Line". 2) Just the shadows with everything else turned off. 3) Just the textures with line work and shadows turned off.
With those three images, layer them in Photoshop so that the linework is the top layer with the blend mode set to "Multiply". The second layer should be the shadow image with the blend mode again set to "Multiply". Finally, the textures layer should be the bottom most layer and the blend mode set to "Normal".
2. The next step was to take the shadows layer and began using the burn tool to create depth in the image. Like I mentioned above, I created a video tutorial a while ago that more clearly explains how this process works. To summarize, I selected individual areas of the shadow with the polygonal tool (you could also turn on the line work layer and use that layer to make selections with the "Magic Wand Tool"). With a selection in place, choose the "Burn Tool" and set the "Range" to "Midtones." Then, using a soft brush with 0% hardness, begin burning the shadow with the darkest areas closest to the object that is casting the shadow. The shadow should get lighter in tone as it moves further from the object casting the shadow. Another way to look at it is to burn a darker shadow wherever you see corners or where there is a change in depth.
You can see in the comparison below that the before and after shows a dramatic change in the quality of shadow. Even without the textures and background, there is a much clearer reading of the geometry.
I also did a quick comparison between the two different shadow options with the textures and background elements inserted. Again, there is much more depth and 3-dimensionality just by spending a little time with the burn tool.
3. After the burning was complete, I selected the texture layer and cut out the background using the "Polygonal Tool" then quickly dropped in some blue tone and faded out trees. Each elevation took about 2 hours to put together. The shadow burning, textures, and background elements took no time at all. Most of my time was actually spent experimenting with the glass. I have yet to come up with a good look for glass in exterior elevations. I ultimately chose to add a small reflection and curtains along with a slight blue tint. I will have to revisit this area later on with a better solution.