First of all: "it’s all his own making" is not idiomatic English. Beter might be something like
The result is of his own making.
After that change, in many contexts either of the two could be used with little change in meaning.
But in my view there is a subtle difference. The phrase "it’s all his own fault" is directly assigning blame. It says that "he" is responsible for the outcome, and he knew or should have known what the result would be.
In contrast, "it's of his own making" says that his actions lead to the result, but says less about blame. It might be that he didn't know and could not reasonably have known what his actions would lead to. So this covers cases that the other phrase does not.