Yes I agree the items in dreams come from thoughts whether conscious or subconscious but the thing is often the items in dreams can be quite unstable. Even if one creates something in a certain way, turn you back on it and then go and look at it and it could of morphed to something else.
Things in dreams are not "stable" and can unexpectively change.
You actually could just never 'turn your back on it' so that it doesn't change, depends on how much awareness you have and the way you structured the dream.
The way I do it is kind of like having a constantly updated map of everything within my head, but not blocking my vision.
If you created every part of your dream, it actually wouldnt really be a dream any more but rather a visualisation. A dream is when ones subconsciousness is also doing much of the creating of the whole thing, hence then just like real life, there is no 100% control over it.
Well dreams already are hallucinations, just while lucid you're controlling the aspects of it.
And you could just create the whole world yourself and not give any jobs to the subcon other then sit in a corner and don't touch =)