A DIY robot dog is mostly a lesson in torque budgeting. The cute videos hide the hard truth: every leg joint fights gravity all the time. If you use weak plastic servos, the robot will stand once, shake, and collapse. Use metal-geared 20-35kg servos or build a much smaller robot.
The approachable design is a 12-DoF quadruped: hip abduction, hip pitch and knee pitch on each leg. The body is a printed or laser-cut rectangle, the legs are short, and the battery sits in the center. Do not copy animal proportions; copy torque-friendly robot proportions with short femurs and tibias.
Start with a static crawl gait before trying dynamic trotting. Add an IMU only after the gait works open-loop. For a first build, the goal is walking reliably on a table, not stairs, grass or jumping. RoboHub can generate the leg geometry and gait scaffold so you spend less time staring at servo angles.