I actually built something similar idea wise just because it seemed like a fun project to play with (http://roofmapper.com). However my implementation was very simplistic in comparison.
That's cool, although I wouldn't rely on the Google map draw tools. It's cool to learn and have personal projects, but advertising yet another data collection tool without a clear idea for where the data is going or if it's even usable seems counter-productive to me, since we have a project like OSM.