Sorry for the late reply.
@ Andy – Ideally you should go on site and take the photo yourself. This way you can measure everything you need. However, in my case that isn’t always possible so I use survey plans or any data I can get my hands on.

@Gutbucket – Even in aerial photos you can take the Z data from nearby buildings, lighting poles, etc.

@K2 – I am sure that you are missing something but I can’t figure out what it is. Have you followed each step of the tutorial?

Just Wondering how you actually do the EXTERIOR photomontage?
Like do you use the Survey plan to create camera points? or do you go to the actual site an get your tape measure out an measure from the point you are taking the picture from?

Sorry, im just very new to this and have to do my first photomontage soon for my boss. bit unsure