i'd attach it to the slab if i were you because that will be less conc to remove when you decide to do this work properly,,, i expect this new roof will stop or divert the water temporarily however it won't be permanent,,, in the meantime the underground waterways will be leading other drainage water down alongside your foundation wall & infiltrating the blocks,,, that wtr will be contaminated w/soil acids ( acid rain, deleterious mtls ) which will & are attacking the lime in the cement which was used to form the blocks,,, in the end, the blocks will rot & collapse.
divorces are so expensive because they're worth it there's also a good reason concrete foundations cost more - they're WORTH IT, TOO ! ! !
in theory, there's no difference between theory & practice,,, in practice, there is,,, some of the responders to this post are theorists !