I would like to get some information on doing a 6 ft retaing wall in my back yard. The goal is to increase my yard size about 12 to 15 feet. My yard has a big hill in the back of it. The span is about wide 65 feet and the angel of the hillside is about 40 to 45 degrees. I want to excavate the hill back about 12 to 15 feet and then build a retaing wall. I don’t have any mason or construction work experience, except for putting in new walls in my garage for an office. However I am very skilled in making things I have very good common sense and I am a real problem solver. I feel very confident I can handle the job, but just need some advise on the technical approach. Any suggestions would help. Thanks