Is it possible to install a terrace roof afterwards?

Can you attach such a canopy to the exterior wall of a prefabricated house?

You need appropriate reinforcement at that spot, alternatively posts attached to the house wall. Even with solid buildings, roofs are not simply hung on the wall; normally one attaches them to the intermediate ceiling. And I never thought I would agree with 11ant on his one-thread policy, but actually around 10 threads in one week do feel a bit much ;)