This was cool.  A little more information about how the game works would have been nice as it took me a while to figure out there were different materials to build with.  This is pretty nostalgic back to Cool "Math" Games which I enjoyed, and the theming is great.  

Unfortunately, the game isn't fully functional.  After the first level, things seem to go downhill.  I'm sure you know this though, only so much you can do in the short time.  My other gripe is the inability (at least as far as I could tell) to switch which node your bridge was coming off of.  This meant I had to backtrack to build some of the things I wanted to, technically laying down duplicate bridges.