I think we can all agree this is not a practical, short-term solution. Even the scientists say it would take 50 years. But this isn't going to blot out the sky, and it isn't going to be much of a platform for displaying ads.

From a practical standpoint, from earth, this thing will be slightly larger than the sun (so it reduces light from the sun over the entire earth). Just like with the sun or the moon, holding your thumb up at arms length will block most or all of it. It will also be fairly transparent, otherwise we would be getting far too little visible light, which would cause other problems. This means actually trying to look at it would be (almost) as inadvisable as looking at the sun. The visual advertising medium you can't look at, can't see details on if you're foolish enough to try, and is the size of your thumb at arms length is neither the sky-blotting structure nor the advertising platform you seem to think it would be.