There are a number of lined textures available. I think the best way is to use some other vector drawing program and export as sharp a picture that you can with png or jpg format. You want a flat view of the texture. If you use SU you have to orient the view to the face and use parallel projection to get a straight-on view, then export at a graphic. Adjust the light and dark sliders in the shadow dialog to get the tone you want for the background (the faces). Using Sketchup doesn't seem the best way to get a texture pattern, in my opinion.