paintmany sided image

I have an image shaped like a house (7 sides). I want to colour each side a few different colors and save painted object as 1 texture file. BY what method/s am I doing this.

I know how to load an texture and color an image etc.

The reason is I need an obj file that can load only 1 texture image for my graphics rendering app i am use.

Multiple ways
UV unwrap the texture and then paint the texture externally such as in photoshop or paint onto the texture directly in blender.
UV unwrap your object, apply different coloured material to each of your objects face and then bake all these colours into your final texture (bake panel in the render settings). Demo

i started another thread as it seems this question has been answered and i have another