I think it's a good implementation of the build system - I haven't played with player placing tiles in any of my games yet as I can't get my head around it haha. The idea of game jams is to learn new mechanics and new things to implement in the future games you make, and for that I'm very pleased for you. The game is a great demonstration of the learning process.
Like others have said, having this as a base mechanic and theme has scope to build up on :)