Building ubuntu classic image with ubuntu-image

Hi, I am trying to build an ubuntu classic image using ubuntu-image. Steps:

git clone -b classic
cd pc-amd64-gadget; snapcraft prime
sudo ubuntu-image classic -d -O out/ -p ubuntu-cpc -a amd64 -s focal <gadget tree>

Problem 1 : when I run snapcraft prime, it does not create a prime directory. So I either need to create a snap, unsquashfs and use squashfs-root as the gadget tree or I need to run snapcraft --shell-after and use the prime directory in the shell to create the classic image.

Problem 2: The resulting pc.img when used for booting a VM, shows a grub shell instead of ubuntu 20.04(passed as suite parameter in the command), which is what I expect. Going through the directories in the shell, I cannot find a vmlinuz or initrd.img anywhere.

Any assistance would be much appreciated.