Trying to build root filesystem in result

so i am trying to build my own iso, but before i convert it to iso, i need to debug it. Is there a way i can do i can generate root filesystem instead of toplevel?

here what i get by using:

cancel@nixos ~> nix build /etc/nixos/buildingIso#nixosConfigurations.exampleIso.config.system.build.toplevel

cancel@nixos ~> ls result
activate init specialisation
bin init-interface-version sw
boot.json initrd switch-inhibitors
dry-activate kernel system
etc kernel-modules systemd
extra-dependencies kernel-params
firmware nixos-version

but it would be preferable to have something like:

ls result/
bin boot dev etc home lib64 mnt nix proc root run srv swap sys tmp usr var