I am building a new home in Melbourne. The site levels on the builder's plans do not match the actual site levels on my land. As such, the builder has excavated considerably more than the building plans specify. This has resulted in a need for a retaining wall solution that I wasn't expecting. The retaining wall needs to be 3m high and 16m long, so considerably expensive with limited options. The building contracts states that retaining walls are my responsibility, but I wouldn't need a retaining wall if the building was built according to the plans. So is the builder at all liable for the retaining wall that I now need to build? And is my neighbour required to contribute to the retaining wall that will be keeping his house from subsiding?