There are many ways to go about this, but the simplest way is to take a picture that is "through the eye of the camera." By this, I mean, take a picture from where you think you will put your camera, if you are using a short throw lens, then take the photo with a wide angle lens, if you are using a zoom lens then take a picture with something between the 24-70mm range. There is an actual way of calculating exactly what mm your lens should be, but in general you want to get a picture of your entire surface, and don't be afraid to stand back a little further and get more of the building. A decent DSLR should have a high enough resolution that if you get more of the building, you can always zoom in and crop it later for what you need. Then in order to make your graphics, you should realign the photo based on the perspective that you think the audience will view it at, or what most people do if they are not playing around with 3D perspectives is to just straighten the building to give After effects a compensated perspective. This tutorial goes over how to do that in photoshop: http://www.madmapper.com/after-effects- ... -building/
I would recommend experimenting with this based on the visuals you are planning to create, as I mentioned before, choosing a specific perspective for 3D is a little bit more of a science but a basic building mapping isn't bad. On top of that, I think the most important piece of this puzzle is your projector. How much ambient light, the lens, and so on. For this tutorial, the photo doesn't matter as much as the amount of ambient light that was on the building: http://projection-mapping.org/tutorial- ... vertising/
Hope that helps somewhat, it's not bad once you get the basics down, but the variables in setup is where the knowledge comes into play.