I like tower defense and your idea is really unique. I think that this is a most interesting idea in this game jam. But implementation is not good.
If ignore bugs i would also suggest some of improvements:
• Do not use tile system to wall positioning. I would prefer free posisiton of wall and ability to rotate wall in y raw. This will give more control for game.
• Display direction for projectiles before building the walls. It will player to understand what to do