Here's a tutorial requested by Master N the Making. It explains how to make your own Super Mario Galaxy planetoids. Please give credit if used.
About this creation
Start with a 2x1 piece with two holes and two small pipes with studs like this.
Make 12 of those no matter how big your planet is.
Collect 6 baseplates.
Collect 6 (not 4) 2x(how long your baseplates are) plates.
Attach the technic pieces like this.
Then you can attach other sides!
It is important with which side you attach those technic pieces...
...because you have to attach those plates to them like this. If you don't do it, the planet'll be fragile.
Attach more pieces like this.
One more plate...
And the all-side-stud cube is ready!
If you want to make round planets, you have to add a lot of plates. Step one.
When you add the decorations, it's a good idea to deattach the baseplate...
...and attach it when it's ready.
Add Mario, enemies, star bits...
To make it "float", first collect a few black baseplates stud down.
Attach them with black bricks.
Attach transparent pieces like this to the bottom side of the planetoid. and attach them to the black baseplates.
The transparent piece you need.