Really fun, and leads to some hilarious builds, or janking your way through a level in a way that was definitely not intended.
Some of the placements were a bit iffy (e.g. the direction the rocket is pointing in the end doesn't always reflect where you placed it, which can be problematic), but for me most part, the building worked pretty well. I'm sure this is a thing you would have included if you had the time, but an undo button would have been really useful. Or at least a way to remove parts (and that way you can also reload the previous build and have the player edit that if they want to, rather than having to start from scratch every time.
Anyway, very enjoyable and great concept. Nicely done!