This leads me to believe you don’t know enough Java/have enough experience with an IDE. Either that or your using code from an ancient version. To change a blocks bounding box, you can override Block#getBoundingBox. However this box can be at maximum 1x1.5x1. Anything bigger than this needs multiple blocks. You can look at how the bed works (probably not the best example for your needs, but looking at vanilla code is always helpful), or at other mods that do similar things.