First you have to use The Google soft "Sketchup 3d" whitch it used to modify 3d object before export to Colada format.
You have lot of 3d model with this soft and you can export in .collada to import in sweethomz3d then.
I made an exemple and i made the textures with my iphone, photoshop..
i shoot that cd box at my work..
and modify
that's all and you do a better job !