You've probably seen those video consoles in home improvement stores or paint suppliers which allow you to apply different paint colours to a house photograph, to see how the colours go together and what the house will look like when painted. They work OK, but there's one big problem. The house they use in the example looks nothing like the one you want to paint.
This exercise shows you how to use Photoshop layer masks and a photograph of your own house to get the same effect. And who knows, the paint shop proprietor might even pay you to do it as a service to clients!
We'll start off with a bit of photographic tweaking and then use a variety of selection tools to select areas and convert them to adjustment layers. Then you can change to colours of your house (within limits) to your heart's content (and so minimise wasted paint!).
First, take your photograph
I'm assuming you have a digital camera, because the process is much easier if you don't have the delay between taking the photo and seeing whether it worked out, and then having to scan it into digital form. However, you can start with a colour print and scan it into Photoshop if you don't have the opportunity to take a photograph directly.
Any reasonably recent digital camera with some form of telephoto and zoom capability is likely to do a satisfactory job. A file size of 1 meg or more is plenty ('High' or 'Super High' quality).
Tip: Time spent taking the photograph well saves a lot of time later.
So, with camera in hand, we walk outside. Is the Sun shining? Are there any tree shadows falling on the house? If so, go back inside again until it's cloudy but bright. This provides uniform illumination that's essential when trying to change the colour of large areas of the image. This is hard enough, without having to deal with shadows and highlights. Figure 1 shows what not to do.
Figure 1. What not to do