I've managed to find a Garry's Mod 13 Beta version. This one is from August, 2012. There was a lot of bugs and other stuff I've needed to fix. The game is still not fully functional.

00:00 - Intro
01:13 - gm_construct
04:30 - Changes to spawn menu
07:07 - gm_flatgrass
08:20 - Building a car
11:48 - Info about the download