Build monitor is a tool which you can use to measure your build times in Visual studio over time. I started this since I noticed my build times increased with a growing code-base and got curious about how much time I spend idle per week/month/year just waiting for the builds, so I can evaluate how much effort I can spend to optimize the builds later on.
It is open source so you are welcome to contribute ( https://github.com/vinntreus/BuildMonitor ).
How it works
When any solution is opened, the extension is loaded and will start output to a output-window called "Build monitor" (Found in View -> Output -> Change "Show output from:" dropdown-list). It measures solution total build time and each project built. After every build the data is also saved to a file on disk (see output-window for path) as json.
Next step is to create a service which uses the data and aggregates and visualize it in some excellent way.