If you would like to create a virtual machine image with the latest build that you have build, execute the following command in the ChromiumOS SDK for the amd64-generic board, if you are building for a different board or a custom board, adjust the board name accordingly.
./image_to_vm.sh --board=amd64-generic
This will create a raw disk image called chromiumos_qemu_image.bin in src/build/images/amd64-generic/latest/. This is a raw disk image that can be booted on QEMU or any other virtualization platform that can run raw disk images.