Cool concept, but I think it would be better if you have another way of building the path, OR if your goal is to let the player build skill to get used to this mechanic that's valid too. Also, add a win and lose condition

Gosh, I really love the idea of building the level as you go. I think I would side the rocket as a boast and make it more tetris style level builder. The only thing I saw that was a major bug was the level builder doesn't adjust to the left and right with the player. Minor improvement would be coyote fly time, there were times where I let go of space bar a little earlier than expected and it just cut off right there causing me to fall to my doom.