Need Help with puzzle design


The basic mechanic is that when the player crosses a tile, the tile turns into a wall, meaning they can't go back to the last tile. So in each room, the goal is for the player to go from the door they entered in, to the next door. I've having a hard time designing levels, because whenever I plan out one it always ends up the same way: a straightforward path to the door, because is essentially making they're own walls. Should I add a second goal, like a key or a button? What would you do to make it better?

Here's the gameplay in action:


There's a bunch of stuff you can do to make the puzzles more complicated. Off the top of my head:
  • You could make it so that you have to collect everything in the level before being able to go through the door (like for example coins).
  • You could also add secondary doors that can only be opened with their corresponding key (yellow door with yellow key, blue door with blue key, ...).
  • Maybe there could be an item that lets you brake though a part of a wall you already made.
  • You could add portals that can only be used once.