If you decide you don't want to roll your own, or are thinking about getting into home automation, you might look at this option:
http://www.amazon.com/GoControl-Linear-GD00Z-4-Z-Wave-Controller/dp/B00M75TEIU
It actually took a price dip today, and according to camelcamelcamel is at its all-time low prime price on Amazon.
I'm using one of these in conjunction with a Smartthings hub, and it works well for me. I also have a TOP-201 camera in the garage to catch motion events and provide a visual confirmation of the door's status.