By Relative pronouns, Accusative

In the first example : which = the house , and my uncle built ( the house )( which ), and since it is an object of the verb built. That means this relative pronoun is in the accusative case. The same goes with the second example. Regarding the third. what = something that, I say something that...

The house which my uncle built cost him US100,000. ( which is the relative pronoun in accusative case ) She is the girl whom I met on the street the other day. ( whom is the relative pronoun in accusative case ) I say what I mean. ( what is the relative pronoun in accusative case )