Download code: https://www.dropbox.com/s/bwha6tr1yw0qtuo/Quadruped_BBD_PS2_4DOF_CODE.zip
Best way to build it yourself is using this set as a starting point: https://www.robotshop.com/en/lynxmotion-sq3u-symmetric-quadruped-walking-robot.html
What I did is add 4 servo's and the code you find in the link. Mine uses 16 HS-645-MG, because of the weight. A also added an accelerometer and 4 footsensors, but you can disable this easily in the code.
Hope this helps.