I'm not an astrophysicist, but since general relativity says matter and energy are related and light can't escape if it crosses the event horizon it would add to the black hole
But a 3m sphere at Jupiter's distance from the sun wouldn't catch much mass equivalent light from the sun
The way we build now is as cheap as will be safe. That's why we have engineers, it takes pretty extensive education to make someone able to make a bridge cheap enough
All the people living in cities